Copyright © 2004 W3C® (MIT, ERCIM, Keio), All Rights Reserved. W3C liability, trademark and document use rules apply.
XML is a versatile markup language, capable of labeling the information content of diverse data sources including structured and semi-structured documents, relational databases, and object repositories. A query language that uses the structure of XML intelligently can express queries across all these kinds of data, whether physically stored in XML or viewed as XML via middleware. This specification describes a query language called XQuery, which is designed to be broadly applicable across many types of XML data sources.
This section describes the status of this document at the time of its publication. Other documents may supersede this document. A list of current W3C publications and the latest revision of this technical report can be found in the W3C technical reports index at http://www.w3.org/TR/.
This is a public W3C Working Draft for review by W3C Members and other interested parties. Publication as a Working Draft does not imply endorsement by the W3C Membership. This is a draft document and may be updated, replaced or obsoleted by other documents at any time. It is inappropriate to cite this document as other than work in progress.
XQuery 1.0 has been defined jointly by the XML Query Working Group and the XSL Working Group (both part of the XML Activity). The XPath 2.0 and XQuery 1.0 Working Drafts are generated from a common source. These languages are closely related, sharing much of the same expression syntax and semantics, and much of the text found in the two Working Drafts is identical.
This working draft includes a number of changes made in response to comments received during the Last Call period that ended on Feb. 15, 2004. The working group is continuing to process these comments, and additional changes are expected. This document reflects decisions taken up to and including the face-to-face meeting in Redmond, WA during the week of August 23, 2004. These decisions are recorded in the Last Call issues list (http://www.w3.org/2004/10/xquery-issues.html). Some of these decisions may not yet have been made in this document. A list of changes introduced by this draft can be found in I Revision Log. The
Note:
A proposal that is currently under discussion would introduce a new form of type promotion, similar to numeric type promotion. Under this proposal, values of type xs:anyURI
would be promotable to the type xs:string
and could therefore be passed to functions such as fn:substring
. One problem with this proposal is that values of type xs:anyURI
are compared on a code-point basis, whereas values of type xs:string
are compared using a
collation. For this reason, promotion of xs:anyURI
to xs:string
might cause value comparison operators such as eq
and gt
to lose their transitive property. This proposal is pending further discussion and is not reflected in this document. However, the signatures of certain functions in [XQuery 1.0 and XPath 2.0 Functions and Operators], such as fn:doc
and fn:QName
, were written with the
expectation that xs:anyURI
would be promotable to xs:string
. The signatures of these functions may change when this issue is resolved.
Public comments on this document and its open issues are invited. Comments should be sent to the W3C XPath/XQuery mailing list, public-qt-comments@w3.org (archived at http://lists.w3.org/Archives/Public/public-qt-comments/), with “[XQuery]” at the beginning of the subject field.
The patent policy for this document is the 5 February 2004 W3C Patent Policy. Patent disclosures relevant to this specification may be found on the XML Query Working Group's patent disclosure page and the XSL Working Group's patent disclosure page. An individual who has actual knowledge of a patent which the individual believes contains Essential Claim(s) with respect to this specification should disclose the information in accordance with section 6 of the W3C Patent Policy.
1 Introduction
2 Basics
2.1 Expression Context
2.1.1 Static Context
2.1.2 Dynamic Context
2.2 Processing Model
2.2.1 Data Model Generation
2.2.2 Schema Import Processing
2.2.3 Expression Processing
2.2.3.1 Static Analysis Phase
2.2.3.2 Dynamic Evaluation Phase
2.2.4 Serialization
2.2.5 Consistency Constraints
2.3 Error Handling
2.3.1 Kinds of Errors
2.3.2 Identifying and Reporting Errors
2.3.3 Handling Dynamic Errors
2.3.4 Errors and Optimization
2.4 Concepts
2.4.1 Document Order
2.4.2 Atomization
2.4.3 Effective Boolean Value
2.4.4 Input Sources
2.5 Types
2.5.1 Predefined Types
2.5.2 Typed Value and String Value
2.5.3 SequenceType Syntax
2.5.4 SequenceType Matching
2.5.4.1 Matching a SequenceType and a Value
2.5.4.2 Matching an ItemType and an Item
2.5.4.3 Element Test
2.5.4.4 Schema Element Test
2.5.4.5 Attribute Test
2.5.4.6 Schema Attribute Test
2.6 Optional Features
2.6.1 Schema Import Feature
2.6.2 Static Typing Feature
2.6.3 Full Axis Feature
2.6.4 Module Feature
2.6.5 XML and Names 1.1 Feature
2.6.6 Pragmas
2.6.7 Must-Understand Extensions
2.6.7.1 XQuery Flagger
2.6.8 Static Typing Extensions
2.6.8.1 XQuery Static Flagger
2.7 Comments
3 Expressions
3.1 Primary Expressions
3.1.1 Literals
3.1.2 Variable References
3.1.3 Parenthesized Expressions
3.1.4 Context Item Expression
3.1.5 Function Calls
3.2 Path Expressions
3.2.1 Steps
3.2.1.1 Axes
3.2.1.2 Node Tests
3.2.2 Predicates
3.2.3 Unabbreviated Syntax
3.2.4 Abbreviated Syntax
3.3 Sequence Expressions
3.3.1 Constructing Sequences
3.3.2 Filter Expressions
3.3.3 Combining Node Sequences
3.4 Arithmetic Expressions
3.5 Comparison Expressions
3.5.1 Value Comparisons
3.5.2 General Comparisons
3.5.3 Node Comparisons
3.6 Logical Expressions
3.7 Constructors
3.7.1 Direct Element Constructors
3.7.1.1 Attributes
3.7.1.2 Namespace Declaration Attributes
3.7.1.3 Content
3.7.1.4 Whitespace in Element Content
3.7.2 Other Direct Constructors
3.7.3 Computed Constructors
3.7.3.1 Computed Element Constructors
3.7.3.2 Computed Attribute Constructors
3.7.3.3 Document Node Constructors
3.7.3.4 Text Node Constructors
3.7.3.5 Computed Processing Instruction Constructors
3.7.3.6 Computed Comment Constructors
3.7.4 In-scope Namespaces of a Constructed Element
3.8 FLWOR Expressions
3.8.1 For and Let Clauses
3.8.2 Where Clause
3.8.3 Order By and Return Clauses
3.8.4 Example
3.9 Ordered and Unordered Expressions
3.10 Conditional Expressions
3.11 Quantified Expressions
3.12 Expressions on SequenceTypes
3.12.1 Instance Of
3.12.2 Typeswitch
3.12.3 Cast
3.12.4 Castable
3.12.5 Constructor Functions
3.12.6 Treat
3.13 Validate Expressions
3.13.1 Validating an Element Node
3.13.2 Validating a Document Node
4 Modules and Prologs
4.1 Version Declaration
4.2 Module Declaration
4.3 Xmlspace Declaration
4.4 Default Collation Declaration
4.5 Base URI Declaration
4.6 Construction Declaration
4.7 Ordering Mode Declaration
4.8 Empty Ordering Declaration
4.9 Inherit-Namespaces Declaration
4.10 Schema Import
4.11 Module Import
4.12 Namespace Declaration
4.13 Default Namespace Declaration
4.14 Variable Declaration
4.15 Function Declaration
A XQuery Grammar
A.1 EBNF
A.1.1 Grammar Notes
A.2 Lexical structure
A.2.1 Terminal Types
A.2.2 Whitespace Rules
A.2.2.1 Default Whitespace Handling
A.2.2.2 Explicit Whitespace Handling
A.2.3 Comments, Pragmas and Extensions
A.3 Reserved Function Names
A.4 Precedence Order
B Type Promotion and Operator Mapping
B.1 Numeric Type Promotion
B.2 Operator Mapping
C Context Components
C.1 Static Context Components
C.2 Dynamic Context Components
C.3 Serialization Parameters
D References
D.1 Normative References
D.2 Non-normative References
D.3 Non-normative Background References
D.4 Non-normative Informative Material
E Summary of Error Conditions
F Glossary (Non-Normative)
G Example Applications (Non-Normative)
G.1 Joins
G.2 Grouping
G.3 Queries on Sequence
G.4 Recursive Transformations
G.5 Selecting Distinct Combinations
H The application/xquery Media Type (Non-Normative)
H.1 Introduction
H.2 Registration of MIME Media Type application/xquery
H.2.1 Interoperability Considerations
H.2.2 Applications Using this Media Type
H.2.3 File Extensions
H.2.4 Intended Usage
H.2.5 Author/Change Controller
H.3 Encoding Considerations
H.4 Recognizing XQuery Files
H.5 Charset Default Rules
H.6 Security Considerations
I Revision Log (Non-Normative)
I.1 23 July 2004
I.2 29 Oct 2004
As increasing amounts of information are stored, exchanged, and presented using XML, the ability to intelligently query XML data sources becomes increasingly important. One of the great strengths of XML is its flexibility in representing many different kinds of information from diverse sources. To exploit this flexibility, an XML query language must provide features for retrieving and interpreting information from these diverse sources.
XQuery is designed to meet the requirements identified by the W3C XML Query Working Group [XML Query 1.0 Requirements] and the use cases in [XML Query Use Cases]. It is designed to be a language in which queries are concise and easily understood. It is also flexible enough to query a broad spectrum of XML information sources, including both databases and documents. The Query Working Group has identified a requirement for both a non-XML query syntax and an XML-based query syntax. XQuery is designed to meet the first of these requirements. XQuery is derived from an XML query language called Quilt [Quilt], which in turn borrowed features from several other languages, including XPath 1.0 [XPath 1.0], XQL [XQL], XML-QL [XML-QL], SQL [SQL], and OQL [ODMG].
[Definition: XQuery operates on the abstract, logical structure of an XML document, rather than its surface syntax. This logical structure, known as the data model, is defined in the [XQuery 1.0 and XPath 2.0 Data Model] document.]
XQuery Version 1.0 is an extension of XPath Version 2.0. Any expression that is syntactically valid and executes successfully in both XPath 2.0 and XQuery 1.0 will return the same result in both languages. Since these languages are so closely related, their grammars and language descriptions are generated from a common source to ensure consistency, and the editors of these specifications work together closely.
XQuery also depends on and is closely related to the following specifications:
[XQuery 1.0 and XPath 2.0 Data Model] defines the data model that underlies all XQuery expressions.
[XQuery 1.0 and XPath 2.0 Formal Semantics] defines the static semantics of XQuery and also contains a formal but non-normative description of the dynamic semantics that may be useful for implementors and others who require a formal definition.
The type system of XQuery is based on [XML Schema].
The default function library and the operators supported by XQuery are defined in [XQuery 1.0 and XPath 2.0 Functions and Operators].
One requirement in [XML Query 1.0 Requirements] is that an XML query language have both a human-readable syntax and an XML-based syntax. The XML-based syntax for XQuery is described in [XQueryX 1.0].
This document specifies a grammar for XQuery, using the same Basic EBNF notation used in [XML 1.0]. Unless otherwise noted (see A.2 Lexical structure), whitespace is not significant in the grammar. Grammar productions are introduced together with the features that they describe, and a complete grammar is also presented in the appendix [A XQuery Grammar]. The appendix is the normative version.
In the grammar productions in this document, nonterminal symbols are underlined and literal text is enclosed in double quotes. Certain productions (including the productions that define DecimalLiteral, DoubleLiteral, and StringLiteral) employ a regular-expression notation. The following example production describes the syntax of a function call:
[85] | FunctionCall |
::= | QName "(" (ExprSingle ("," ExprSingle)*)? ")" |
The production should be read as follows: A function call consists of a QName followed by an open-parenthesis. The open-parenthesis is followed by an optional argument list. The argument list (if present) consists of one or more expressions, separated by commas. The optional argument list is followed by a close-parenthesis.
Certain aspects of language processing are described in this specification as implementation-defined or implementation-dependent.
[Definition: Implementation-defined indicates an aspect that may differ between implementations, but must be specified by the implementor for each particular implementation.]
[Definition: Implementation-dependent indicates an aspect that may differ between implementations, is not specified by this or any W3C specification, and is not required to be specified by the implementor for any particular implementation.]
This document normatively defines the dynamic semantics of XQuery. The static semantics of XQuery are normatively defined in [XQuery 1.0 and XPath 2.0 Formal Semantics]. In this document, examples and material labeled as "Note" are provided for explanatory purposes and are not normative.
The basic building block of XQuery is the expression, which is a string of [Unicode] characters. The language provides several kinds of expressions which may be constructed from keywords, symbols, and operands. In general, the operands of an expression are other expressions. [Definition: XQuery is a functional language, which means that expressions can be nested with full generality. (However, unlike a pure functional language, it does not allow variable substitutability if the variable declaration contains construction of new nodes.)] [Definition: XQuery is also a strongly-typed language in which the operands of various expressions, operators, and functions must conform to the expected types.]
Note:
This specification contains no assumptions or requirements regarding the character set encoding of strings of [Unicode] characters.
Like XML, XQuery is a case-sensitive language. Keywords in XQuery use lower-case characters and are not reserved—that is, names in XQuery expressions are allowed to be the same as language keywords—except for the list of reserved function-names in A.3 Reserved Function Names.
[Definition: In the data model, a value is always a sequence.] [Definition: A sequence is an ordered collection of zero or more items.] [Definition: An item is either an atomic value or a node.] [Definition: An atomic value is a value in the value space of an atomic type, including all the atomic types defined in [XML Schema], and three additional atomic types: xdt:dayTimeDuration, xdt:yearMonthDuration, and xdt:untypedAtomic.] [Definition: A node is an instance of one of the node kinds defined in [XQuery 1.0 and XPath 2.0 Data Model].] Each node has a unique node identity, a typed value, and a string value. In addition, some nodes have a name. The typed value of a node is a
sequence of zero or more atomic values. The string value of a node is a value of type xs:string
. The name of a node is a value of type xs:QName
.
[Definition: A sequence containing exactly one item is called a singleton sequence.] An item is identical to a singleton sequence containing that item. Sequences are never nested—for example, combining the values 1, (2, 3), and ( ) into a single sequence results in the sequence (1, 2, 3). [Definition: A sequence containing zero items is called an empty sequence.]
[Definition: The term data model instance is used, synonymously with the term value, to denote an unconstrained sequence of nodes and/or atomic values.]
Names in XQuery are called QNames, and conform to the syntax in [XML Names]. [Definition: Lexically, a QName consists of an optional namespace prefix and a local name. If the namespace prefix is present, it is separated from the local name by a colon.] A lexical QName can be converted into an expanded QName by resolving its namespace prefix to a namespace URI, as described later in this document. [Definition: An expanded QName consists of an optional namespace URI and a local name. An expanded QName also retains its original namespace prefix (if any), to facilitate casting the expanded QName into a string.] Two expanded QNames are equal if their namespace URIs are equal and their local names are equal (even if their namespace prefixes are not equal). Namespace URIs and local names are compared on a codepoint basis, without normalization.
Certain namespace prefixes are predeclared by XQuery and bound to fixed namespace URIs. These namespace prefixes are as follows:
xml = http://www.w3.org/XML/1998/namespace
xs = http://www.w3.org/2001/XMLSchema
xsi = http://www.w3.org/2001/XMLSchema-instance
fn = http://www.w3.org/2004/10/xpath-functions
xdt = http://www.w3.org/2004/10/xpath-datatypes
local = http://www.w3.org/2004/10/xquery-local-functions
(see 4.15 Function Declaration.)
In addition to the prefixes in the above list, this document uses the prefix err
to represent the namespace URI http://www.w3.org/2004/10/xqt-errors
(see 2.3.2 Identifying and Reporting Errors). This namespace prefix is not predeclared and its use in this document is not normative.
In some cases, where the meaning is clear and namespaces are not important to the discussion, built-in XML Schema typenames such as integer
and string
are used without a namespace prefix.
Element nodes have a property called in-scope namespaces. [Definition: The in-scope namespaces property of an element node is a set of namespace bindings, each of which associates a namespace prefix with a URI, thus defining the set of namespace prefixes that are available for interpreting QNames within the scope of the element. For a given element, one namespace binding may have an empty prefix; the URI of this namespace binding is the default namespace within the scope of the element.]
Note:
In [XPath 1.0], the in-scope namespaces of an element node are represented by a collection of namespace nodes arranged on a namespace axis, which is optional and deprecated in [XPath 2.0]. XQuery does not support the namespace axis and does not represent namespace bindings in the form of nodes. However, where other specifications such as [XSLT 2.0 and XQuery 1.0 Serialization] refer to namespace nodes, these nodes may be synthesized from the in-scope namespaces of an element node by interpreting each namespace binding as a namespace node.
[Definition: The expression context for a given expression consists of all the information that can affect the result of the expression.] This information is organized into two categories called the static context and the dynamic context.
[Definition: The static context of an expression is the information that is available during static analysis of the expression, prior to its evaluation.] This information can be used to decide whether the expression contains a static error. If analysis of an expression relies on some component of the static context that has not been assigned a value, a static error is raised.[err:XP0001]
The individual components of the static context are summarized below. Further rules governing the semantics of these components can be found in C.1 Static Context Components.
[Definition: XPath 1.0 compatibility mode. This component must be set by all host languages that include XPath 2.0 as a subset, indicating whether rules for compatibility with XPath 1.0 are in effect. XQuery sets the value of this component to false
. ]
[Definition: Statically known namespaces. This is a set of (prefix, URI) pairs that define all the namespaces that are known during static processing of a given expression.] Note the difference between in-scope namespaces, which is a dynamic property of an element node, and statically known namespaces, which is a static property of an expression.
Some namespaces are predefined; additional namespaces can be added to the statically known namespaces by namespace declarations in a Prolog and by namespace declaration attributes in direct element constructors.
[Definition: Default element/type namespace. This is a namespace URI or "none". The namespace URI, if present, is used for any unprefixed QName appearing in a position where an element or type name is expected.] The initial default element/type namespace may be provided by the external environment or by a declaration in a Prolog.
[Definition: Default function namespace. This is a namespace URI that is used for any unprefixed QName appearing as the function name in a function call. The initial default function namespace may be provided by the external environmentor by a declaration in a Prolog.]
[Definition: In-scope schema definitions. This is a generic term for all the element, attribute, and type definitions that are in scope during processing of an expression.] It includes the following three parts:
[Definition: In-scope type definitions. Each type definition is identified either by an expanded QName (for a named type) or by an implementation-dependent type identifier (for an anonymous type). The in-scope type definitions include the predefined types described in 2.5.1 Predefined Types. If the Schema Import Feature is supported, in-scope type definitions also include all type definitions found in imported schemas. ]
[Definition: In-scope element declarations. Each element declaration is identified either by an expanded QName (for a top-level element declaration) or by an implementation-dependent element identifier (for a local element declaration). If the Schema Import Feature is supported, in-scope element declarations include all element declarations found in imported schemas. ] An element declaration includes information about the element's substitution group affiliation.
[Definition: Substitution groups are defined in [XML Schema] Part 1, Section 2.2.2.2. Informally, the substitution group headed by a given element (called the head element) consists of the set of elements that can be substituted for the head element without affecting the outcome of schema validation.]
[Definition: In-scope attribute declarations. Each attribute declaration is identified either by an expanded QName (for a top-level attribute declaration) or by an implementation-dependent attribute identifier (for a local attribute declaration). If the Schema Import Feature is supported, in-scope attribute declarations include all attribute declarations found in imported schemas.]
[Definition: In-scope variables. This is a set of (expanded QName, type) pairs. It defines the set of variables that are available for reference within an expression. The expanded QName is the name of the variable, and the type is the static type of the variable.]
Variable declarations in a Prolog are added to in-scope variables. An expression that binds a variable (such as a let
, for
, some
, or every
expression) extends the in-scope
variables of its subexpressions with the new bound variable and its type. Within a function declaration, the in-scope variables are extended by the names and types of the function parameters.
The static type of a variable may be either declared in a query or (if the Static Typing Feature is enabled) inferred by static type inference rules as described in [XQuery 1.0 and XPath 2.0 Formal Semantics].
Context item static type. This component defines the static type of the context item within the scope of a given expression.
[Definition: Function signatures. This component defines the set of functions that are available to be called from within an expression. Each function is uniquely identified by its expanded QName and its arity (number of parameters).] In addition to the name and arity, each function signature specifies the static types of the function parameters and result.
The function signatures include the signatures of constructor functions, which are discussed in 3.12.5 Constructor Functions.
[Definition: Statically known collations. This is a set of (URI, collation) pairs. It defines the names of the collations that are available for use in function calls that take a collation name as an argument.] [Definition: A collation is a specification of the manner in which character strings are compared and, by extension, ordered. For a more complete definition of collation, see [XQuery 1.0 and XPath 2.0 Functions and Operators].]
[Definition: Default collation. This identifies one of the collations in statically known collations as the collation to be used by string comparison functions and operators when no explicit collation is specified.]
[Definition: Construction mode. The construction mode governs the behavior of element constructors. If construction mode is preserve
, the type of a constructed element node is xs:anyType
, and the attributes and descendants of the constructed element retain their original types. If construction mode is strip
, the type of the constructed element node and all its descendants
is xdt:untyped
, and attributes of the constructed element have type xdt:untypedAtomic
.]
[Definition: Ordering mode. Ordering mode, which has the value ordered
or unordered
, affects the ordering of the result sequence returned by path expressions, union
, intersect
, and except
expressions, and FLWOR expressions that have no order by
clause.] Details are provided in the descriptions of these expressions.
[Definition: Default ordering for empty sequences. This component controls whether an empty sequence is interpreted as the greatest value or as the least value during processing of an order by
clause in a FLWOR expression, as described in 3.8.3 Order By and Return Clauses.] Its value may be greatest
or
least
.
[Definition: XMLSpace policy. This component controls the processing of whitespace by element constructors, as described in 3.7.1.4 Whitespace in Element Content.] Its value may be preserve
or strip
.
[Definition: Namespace inheritance mode. This component controls the namespace bindings that are inherited when an existing element node is copied by an element constructor, as described in 3.7.1 Direct Element Constructors. Its value may be yes
or no
.]
[Definition: Base URI. This is an absolute URI, used when necessary in the resolution of relative URIs (for example, by the fn:resolve-uri
function.)]
[Definition: Statically known documents. This is a mapping from strings onto types. The string represents the absolute URI of a resource that is potentially available using the fn:doc
function. The type is the static type of a call to fn:doc
with the given URI as its literal argument. ] If the argument to fn:doc
is a string literal that is not present in statically known
documents, then the static type of fn:doc
is document-node()?
.
Note:
The purpose of the statically known documents is to provide static type information, not to determine which documents are available. A URI need not be found in the statically known documents to be accessed using fn:doc
.
[Definition: Statically known collections. This is a mapping from strings onto types. The string represents the absolute URI of a resource that is potentially available using the fn:collection
function. The type is the type of the sequence of nodes that would result from calling the fn:collection
function with this URI as its argument.] If the argument to
fn:collection
is a string literal that is not present in statically known collections, then the static type of fn:collection
is node()*
.
Note:
The purpose of the statically known collections is to provide static type information, not to determine which collections are available. A URI need not be found in the statically known collections to be accessed using fn:collection
.
[Definition: Statically known default collection type. This is the type of the sequence of nodes that would result from calling the fn:collection
function with no arguments.] Unless initialized to some other value by an implementation, the value of statically known default collection type is node()*
.
XQuery Flagger status. This component has the value "on
" if the XQuery Flagger is implemented and enabled; otherwise it has the value "off
".
XQuery Static Flagger status. This component has the value "on
" if the XQuery Static Flagger is implemented and enabled; otherwise it has the value "off
".
[Definition: The dynamic context of an expression is defined as information that is available at the time the expression is evaluated.] If evaluation of an expression relies on some part of the dynamic context that has not been assigned a value, a dynamic error is raised.[err:XP0002]
The individual components of the dynamic context are summarized below. Further rules governing the semantics of these components can be found in C.2 Dynamic Context Components.
The dynamic context consists of all the components of the static context, and the additional components listed below.
[Definition: The first three components of the dynamic context (context item, context position, and context size) are called the focus of the expression. ] The focus enables the processor to keep track of which items are being processed by the expression.
Certain language constructs, notably the path expression E1/E2
and the filter expression E1[E2]
, create a new focus for the evaluation of a sub-expression. In these constructs, E2
is evaluated once for each item in the sequence that results from evaluating E1
. Each time E2
is evaluated, it is evaluated with a different focus. The focus for evaluating E2
is referred to below as the inner focus, while the focus for
evaluating E1
is referred to as the outer focus. The inner focus exists only while E2
is being evaluated. When this evaluation is complete, evaluation of the containing expression continues with its original focus unchanged.
[Definition: The context item is the item currently being processed. An item is either an atomic value or a node.][Definition: When the context item is a node, it can also be referred to as the context node.] The context item is returned by the expression ".
". When an expression E1/E2
or E1[E2]
is evaluated,
each item in the sequence obtained by evaluating E1
becomes the context item in the inner focus for an evaluation of E2
.
[Definition: The context position is the position of the context item within the sequence of items currently being processed.] It changes whenever the context item changes. Its value is always an integer greater than zero. The context position is returned by the expression fn:position()
. When an expression E1/E2
or E1[E2]
is evaluated, the context position in the inner focus
for an evaluation of E2
is the position of the context item in the sequence obtained by evaluating E1
. The position of the first item in a sequence is always 1 (one). The context position is always less than or equal to the context size.
[Definition: The context size is the number of items in the sequence of items currently being processed.] Its value is always an integer greater than zero. The context size is returned by the expression fn:last()
. When an expression E1/E2
or E1[E2]
is evaluated, the context size in the inner focus for an evaluation of E2
is the number of items in the sequence obtained by
evaluating E1
.
[Definition: Variable values. This is a set of (expanded QName, value) pairs. It contains the same expanded QNames as the in-scope variables in the static context for the expression. The expanded QName is the name of the variable and the value is the dynamic value of the variable, which includes its dynamic type.]
[Definition: Function implementations. Each function in function signatures has a function implementation that enables the function to map instances of its parameter types into an instance of its result type. For a user-defined function, the function implementation is an XQuery expression. For a built-in function or external function, the function implementation is implementation-dependent.]
[Definition: Current dateTime. This information represents an implementation-dependent point in time during the processing of a query, and includes an explicit timezone. It can be retrieved by the fn:current-dateTime
function. If invoked multiple times during the execution of a query, this function always returns the same result.]
[Definition: Implicit timezone. This is the timezone to be used when a date, time, or dateTime value that does not have a timezone is used in a comparison or arithmetic operation. The implicit timezone is an implementation-defined value of type xdt:dayTimeDuration
. See [ISO 8601] for the range of legal values of a
timezone.]
[Definition: Available documents. This is a mapping of strings onto document nodes. The string represents the absolute URI of a resource. The document node is the root of a tree that represents that resource using the data model. The document node is returned by the fn:doc
function when applied to that URI.] The set of available documents is not
constrained by the set of statically known documents, and it may be empty.
[Definition: Available collections. This is a mapping of strings onto sequences of nodes. The string represents the absolute URI of a resource. The sequence of nodes represents the result of the fn:collection
function when that URI is supplied as the argument. ] The set of available collections is not constrained by the set of statically known collections, and it may be empty.
[Definition: Default collection. This is the sequence of nodes that would result from calling the fn:collection
function with no arguments.] The value of default collection must be initialized by the implementation.
XQuery is defined in terms of the data model and in terms of the expression context.
Figure 1: Processing Model Overview
Figure 1 provides a schematic overview of the processing steps that are discussed in detail below. Some of these steps are completely outside the domain of XQuery; in Figure 1, these are depicted outside the line that represents the boundaries of the language, an area labeled external processing. The external processing domain includes generation of a data model instance that represents the data to be queried (see 2.2.1 Data Model Generation), schema import processing (see 2.2.2 Schema Import Processing) and serialization (see 2.2.4 Serialization). The area inside the boundaries of the language is known as the query processing domain, which includes the static analysis and dynamic evaluation phases (see 2.2.3 Expression Processing). Consistency constraints on the query processing domain are defined in 2.2.5 Consistency Constraints.
Before a query can be processed, its input data must be represented as a data model instance. This process occurs outside the domain of XQuery, which is why Figure 1 represents it in the external processing domain. Here are some steps by which an XML document might be converted to a data model instance:
A document may be parsed using an XML parser that generates an XML Information Set (see [XML Infoset]). The parsed document may then be validated against one or more schemas. This process, which is described in [XML Schema], results in an abstract information structure called the Post-Schema Validation Infoset (PSVI). If a document has no associated schema, its Information Set is preserved. (See DM1 in Fig. 1.)
The Information Set or PSVI may be transformed into a data model instance by a process described in [XQuery 1.0 and XPath 2.0 Data Model]. (See DM2 in Fig. 1.)
The above steps provide an example of how a data model instance might be constructed. A data model instance might also be synthesized directly from a relational database, or constructed in some other way (see DM3 in Fig. 1.) XQuery is defined in terms of the data model, but it does not place any constraints on data model instances are constructed.
[Definition: Each atomic value, element node, and attribute node in a data model instance has a dynamic type. The dynamic type specifies a range of values—for example, an attribute named version
might have the dynamic type xs:decimal
, indicating that it contains a decimal value.]
[Definition: The type annotation of an element or attribute node is an implementation-dependent representation of its dynamic type.] If the data model instance was derived from an validated XML document as described in [XQuery 1.0 and XPath 2.0 Data Model], the type annotations of the element and attribute nodes are derived from schema validation. XQuery does not provide a way to directly access the type annotation of an element or attribute node.
The value of an attribute is represented directly within the attribute node. An attribute node whose type is unknown (such as might occur in a schemaless document) is annotated with the dynamic type xdt:untypedAtomic
.
The value of an element is represented by the children of the element node, which may include text nodes and other element nodes. The dynamic type of an element node indicates how the values in its child text nodes are to be interpreted. An element that has not been validated (such as might occur in a schemaless document) is annotated with the type xdt:untyped
. An element that has been validated and found to be partially valid is annotated with the type xs:anyType
. If an
element node is annotated xdt:untyped
, all its descendant element nodes are also annotated xdt:untyped
. However, if an element node is annotated xs:anyType
, some of its descendant element nodes may have a more specific type annotation.
An atomic value of unknown type is annotated with the type xdt:untypedAtomic
.
The in-scope schema definitions in the static context may be extracted from actual XML schemas as described in [XQuery 1.0 and XPath 2.0 Formal Semantics] (see step SI1 in Figure 1) or may be generated by some other mechanism (see step SI2 in Figure 1). In either case, the result must satisfy the consistency constraints defined in 2.2.5 Consistency Constraints.
XQuery defines two phases of processing called the static analysis phase and the dynamic evaluation phase (see Fig. 1). During the static analysis phase, static errors or type errors may be raised. During the dynamic evaluation phase, dynamic errors or type errors may be raised. These kinds of errors are defined in 2.3.1 Kinds of Errors.
In processing an expression, an implementation is free to use any strategy or algorithm whose result conforms to the specifications in this document.
[Definition: The static analysis phase depends on the expression itself and on the static context. The static analysis phase does not depend on input data (other than schemas).]
During the static analysis phase, the query is parsed into an internal representation called the operation tree (step SQ1 in Figure 1). A parse error is raised as a static error.[err:XP0003] The static context is initialized by the implementation (step SQ2). The static context is then changed and augmented based on information in the prolog (step SQ3). If the Schema Import Feature is supported, the in-scope schema definitions are populated with information from imported schemas. If the Module Feature is supported, the static context is extended with function declarations and variable declarations from imported modules. The static context is used to resolve type names, function names, namespace prefixes, and variable names (step SQ4). If a name in the operation tree is not found in the static context, a static error [err:XP0008] is raised (however, see exceptions to this rule in 2.5.4.3 Element Test and 2.5.4.5 Attribute Test.)
The operation tree is then normalized by making explicit the implicit operations such as atomization, numeric type promotion, and extraction of Effective Boolean Values (step SQ5). The normalization process is described in [XQuery 1.0 and XPath 2.0 Formal Semantics].
If the Static Typing Feature is supported, each expression is assigned a static type (step SQ6). [Definition: The static type of an expression may be either a named type or a structural description—for example, xs:boolean?
denotes an optional occurrence of the xs:boolean
type.
The rules for inferring the static types of various expressions are described in [XQuery 1.0 and XPath 2.0 Formal Semantics].] In some cases, the static type is derived from the lexical form of the expression; for example, the static type of the literal 5
is xs:integer
. In other cases, the
static type of an expression is inferred according to rules based on the static types of its operands; for example, the static type of the expression 5 + 1.2
is xs:decimal
.
During the static analysis phase, if the Static Typing Feature is in effect and an operand of an expression is found to have a static type that is not appropriate for that operand, a type error is raised.[err:XP0004] If static type checking raises no errors and assigns a static type T to an expression, then execution of the expression on valid input data is guaranteed either to produce a value of type T or to raise a dynamic error.
During the static analysis phase, if the Static Typing Feature is in effect and the static type assigned to an expression other than ()
or data(())
is empty()
, a static error is raised.[err:XP0005] This catches cases in which a query refers to an element or attribute that is not present in the in-scope schema definitions, possibly because of a spelling error.
The purpose of the Static Typing Feature is to provide early detection of type errors and to infer type information that may be useful in optimizing the evaluation of an expression.
[Definition: The dynamic evaluation phase is the phase during which the value of an expression is computed.] It occurs after completion of the static analysis phase.
The dynamic evaluation phase can occur only if no errors were detected during the static analysis phase. If the Static Typing Feature is in effect, all type errors are detected during static analysis and serve to inhibit the dynamic evaluation phase. If the Static Typing Feature is not in effect, an implementation is allowed to raise type-related warnings during the static analysis phase. It may then proceed with the dynamic evaluation phase; in this case, type errors must be detected and raised during dynamic evaluation.
The dynamic evaluation phase depends on the operation tree of the expression being evaluated (step DQ1), on the input data (step DQ4), and on the dynamic context (step DQ5), which in turn draws information from the external environment (step DQ3) and the static context (step DQ2). Execution of the evaluation phase may create new data-model values (step DQ4) and it may extend the dynamic context (step DQ5)—for example, by binding values to variables.
A dynamic type is associated with each value as it is computed. The dynamic type of a value may be more specific than the static type of the expression that computed it (for example, the static type of an expression might be "zero or more integers," but at evaluation time its value may have the dynamic type "integer.")
If an operand of an expression is found to have a dynamic type that is not appropriate for that operand, a type error is raised.[err:XP0006]
Even though static typing can catch many type errors before an expression is executed, it is possible for an expression to raise an error during evaluation that was not detected by static analysis. For example, an expression may contain a cast of a string into an integer, which is statically valid. However, if the actual value of the string at run time cannot be cast into an integer, a dynamic error
will result. Similarly, an expression may apply an arithmetic operator to a value whose static type is xdt:untypedAtomic
. This is not a static error, but at run time, if the value cannot be successfully cast to a numeric type, a dynamic error will be raised.
When the Static Typing Feature is in effect, it is also possible for static analysis of an expression to raise a type error, even though execution of the expression on certain inputs would be successful. For example, an expression might contain a function that requires an element as its parameter, and the static analysis phase might infer the static type of the function parameter to be an optional element. This case is treated as a type error and inhibits evaluation, even though the function call would have been successful for input data in which the optional element is present.
[Definition: Serialization is the process of converting a data model instance into a sequence of octets (step DM4 in Figure 1.) ] The general framework for serialization is described in [XSLT 2.0 and XQuery 1.0 Serialization].
An XQuery implementation is not required to provide a serialization interface. For example, an implementation may only provide a DOM interface (see [Document Object Model]) or an interface based on an event stream. In these cases, serialization would be outside of the scope of this specification.
[XSLT 2.0 and XQuery 1.0 Serialization] defines a set of serialization parameters that govern the serialization process. If an XQuery implementation provides a serialization interface, it may support (and may expose to users) any of the serialization parameters listed (with default values) in C.3 Serialization Parameters. An XQuery implementation that provides a serialization interface must support
some combination of serialization parameters in which method = "xml"
and version = "1.0"
.
Note:
The data model permits an element node to have fewer in-scope namespaces than its parent. Correct serialization of such an element node would require "undeclaration" of namespaces, which is a feature of [XML Names 1.1]. An implementation that does not support the XML and Names 1.1 Feature is permitted to serialize such an element without "undeclaration" of namespaces, which effectively causes the element to inherit the in-scope namespaces of its parent.
In order for XQuery to be well defined, the input data model instance, the static context, and the dynamic context must be mutually consistent. The consistency constraints listed below are prerequisites for correct functioning of an XQuery implementation. Enforcement of these consistency constraints is beyond the scope of this specification. This specification does not define the result of a query under any condition in which one or more of these constraints is not satisfied.
Some of the consistency constraints use the term data model schema. [Definition: For a given node in a data model instance, the data model schema is defined as the schema from which the type annotation of that node was derived.] For a node that was constructed by some process other than schema validation, the data model schema consists simply of the type definition that is represented by the type annotation of the node.
For every node that has a type annotation, if that type annotation is found in the in-scope schema definitions (ISSD), then its definition in the ISSD must be the same as its definition in the data model schema. Furthermore, all types that are derived by extension from the given type in the data model schema must also be known by equivalent definitions in the ISSD.
For every element name EN that is found both in a data model instance and in the in-scope schema definitions (ISSD), all elements that are known in the data model schema to be in the substitution group headed by EN must also be known in the ISSD to be in the substitution group headed by EN.
Every item type (i.e., every element, attribute, or type name) referenced in in-scope variables or function signatures must be in the in-scope schema definitions.
For each mapping of a string to a document node in available documents, if there exists a mapping of the same string to a document type in statically known documents, the document node must match the document type, using the matching rules in 2.5.4 SequenceType Matching.
For each mapping of a string to a sequence of nodes in available collections, if there exists a mapping of the same string to a type in statically known collections, the sequence of nodes must match the type, using the matching rules in 2.5.4 SequenceType Matching.
For each (variable, type) pair in in-scope variables and the corresponding (variable, value) pair in variable values such that the variable names are equal, the value must match the type, using the matching rules in 2.5.4 SequenceType Matching.
For each variable declared as external
: If the variable declaration includes a declared type, the external environment must provide a value for the variable that matches the declared type, using the matching rules in 2.5.4 SequenceType Matching. If the variable declaration does not include a declared type, the external environment must provide a type and a matching value, using the same matching rules.
For a given query, define a participating ISSD as the in-scope schema definitions of a module that is used in evaluating the query. If two participating ISSDs contain a definition for the same type name, element name, or attribute name, the definitions must be equivalent in both ISSDs. Furthermore, if two participating ISSDs each contain a definition of a type name T, the set of types derived by extension from T must be equivalent in both ISSDs. Also, if two participating ISSDs each contain a definition of an element name E, the substitution group headed by E must be equivalent in both ISSDs.
As described in 2.2.3 Expression Processing, XQuery defines an analysis phase, which does not depend on input data, and an evaluation phase, which does depend on input data. Errors may be raised during each phase.
[Definition: A static error is an error that must be detected during the analysis phase. A syntax error is an example of a static error. The means by which static errors are reported during the analysis phase is implementation-defined. ]
[Definition: A dynamic error is an error that must be detected during the evaluation phase and may be detected during the analysis phase. Numeric overflow is an example of a dynamic error. ]
[Definition: A type error may be raised during the analysis or evaluation phase. During the analysis phase, a type error occurs when the static type of an expression does not match the expected type of the context in which the expression occurs. During the evaluation phase, a type error occurs when the dynamic type of a value does not match the expected type of the context in which the value occurs. ]
The outcome of the analysis phase is either success or one or more type errors and/or static errors. The result of the evaluation phase is either a result value, a type error, or a dynamic error.
If any expression (at any level) can be evaluated during the analysis phase (because all its explicit operands are known and it has no dependencies on the dynamic context), then any error in performing this evaluation may be reported as a static error. However, the fn:error()
function must not be evaluated during the analysis phase. For example, an implementation is allowed (but not required) to treat the following expression as a static error, because it calls a constructor function with a
constant string that is not in the lexical space of the target type:
xs:date("Next Tuesday")
If the Static Typing Feature is not in effect but an implementation can nevertheless determine during the analysis phase that an expression will necessarily raise a type error, the implementation may report that error during the analysis phase.
In addition to static errors, dynamic errors, and type errors, an XQuery implementation may raise warnings, either during the analysis phase or the evaluation phase. The circumstances in which warnings are raised, and the ways in which warnings are handled, are implementation-defined.
In addition to the errors defined in this specification, an implementation may raise a dynamic error if insufficient resources are available for processing a given expression. For example, an implementation may specify limitations on the maximum numbers or sizes of various objects. These limitations, and the consequences of exceeding them, are implementation-dependent.
The errors defined in this specification are identified by QNames that have the form err:XXYYnnnn
, where:
err
denotes the namespace for XPath and XQuery errors, http://www.w3.org/2004/10/xqt-errors
. This binding of the namespace prefix err
is used for convenience in this document, and is not normative.
XX
denotes the language in which the error is defined, using the following encoding:
XP
denotes an error defined by XPath. Such an error may also occur XQuery since XQuery includes XPath as a subset.
XQ
denotes an error defined by XQuery.
YY
denotes the error category, using the following encoding:
ST
denotes a static error.
DY
denotes a dynamic error.
TY
denotes a type error.
nnnn
is a unique numeric code.
Note:
The namespace URI for XPath and XQuery errors is not expected to change from one version of XQuery to another. However, the contents of this namespace may be extended to include additional error definitions.
An error, if it occurs, is reported to the external processing environment in the form of a URI reference that is derived from the error QName. An error QName with namespace URI NS
and local part LP
will be returned as the URI reference NS
#
LP
. The method by which the URI reference is returned to the external processing environment is implementation-defined.
As an example, an error identified in this document as err:XPST0017
would be returned to the external processing environment as http://www.w3.org/2004/10/xqt-errors#XPST0017
.
Note:
Implementations may also wish to return additional information, such as the location of the error. If an implementation chooses to do so, then the mechanism that it uses to return this information is implementation-defined.
Except as noted in this document, if any operand of an expression raises a dynamic error, the expression also raises a dynamic error. If an expression can validly return a value or raise a dynamic error, the implementation may choose to return the value or raise the dynamic error. For example, the logical expression expr1 and expr2
may return the value false
if either
operand returns false
, or may raise a dynamic error if either operand raises a dynamic error.
If more than one operand of an expression raises an error, the implementation may choose which error is raised by the expression. For example, in this expression:
($x div $y) + xs:decimal($z)
both the sub-expressions ($x div $y)
and xs:decimal($z)
may raise an error. The implementation may choose which error is raised by the "+
" expression. Once one operand raises an error, the implementation is not required, but is permitted, to evaluate any other operands.
A dynamic error is identified by a QName, and may also carry a descriptive string and one or more additional values called error values. An implementation may provide a mechanism whereby an application-defined error handler can process error values and produce diagnostic messages.
A dynamic error may be raised by a built-in function or operator. For example, the div
operator raises an error if its operands are xs:decimal
values and its second operand is equal to zero. Errors raised by built-in functions and operators are defined in [XQuery 1.0 and XPath 2.0 Functions and Operators].
A dynamic error can also be raised explicitly by calling the fn:error
function, which only raises an error and never returns a value. This function is defined in [XQuery 1.0 and XPath 2.0 Functions and Operators]. For example, the following function call raises a dynamic error, providing a QName that identifies the error, a descriptive string, and a diagnostic value:
fn:error(QName("app:err057"), "Unexpected value", fn:string($v))
Because different implementations may choose to evaluate or optimize an expression in different ways, certain aspects of the detection and reporting of dynamic errors are implementation-dependent, as described in this section.
When an implementation is able to evaluate an expression without evaluating some subexpression, the implementation is never required to evaluate that subexpression solely to determine whether it raises a dynamic error. For example, if a function parameter is never used in the body of the function, an implementation may choose whether to evaluate the expression bound to that parameter in a function call.
Similarly, in evaluating an expression, an implementation is not required to search for data whose only possible effect on the result would be to raise an error, as illustrated in the following examples.
If an implementation can find (for example, by using an index) that at least one item returned by $expr1
in the following example has the value 47
, it is allowed to return true
as the result of the some
expression, without searching for another item returned by $expr1
that would raise an error if it were evaluated.
some $x in $expr1 satisfies $x = 47
In the following example, if an implementation can find (for example, by using an index) the product
element-nodes that have an id
child with the value 47
, it is allowed to return these nodes as the result of the path expression, without searching for another product
node that would raise an error because it has an id
child whose value is not an integer.
//product[id = 47]
An implementation is always free to evaluate the operands of an operator in any order.
In some cases, an optimizer may be able to achieve substantial performance improvements by rearranging an expression so that the underlying operations are performed in a different order than that in which they are written. In such cases, errors may be raised that would not have been raised if the expression were evaluated as written. However, an expression must not be rearranged in a way that changes its result value in the absence of errors.
The expression in the following example cannot raise a casting error if it is evaluated exactly as written (i.e., left to right). An implementation is permitted, however, to reorder the predicates to achieve better performance (for example, by taking advantage of an index). This reordering could cause the expression to raise an error.
$N[@x castable as xs:date][xs:date(@x) gt xs:date("2000-01-01")]
To avoid unexpected errors caused by reordering of expressions, tests that are designed to prevent dynamic errors should be expressed using conditional or typeswitch
expressions. Conditional and typeswitch
expressions raise only dynamic errors that occur in the branch that is actually selected.
Unlike the previous example, the following example cannot raise a dynamic error if @x
is not castable into an xs:date
.
$N[if (@x castable as xs:date) then xs:date(@x) gt xs:date("2000-01-01") else false()]
This section explains some concepts that are important to the processing of XQuery expressions.
An ordering called document order is defined among all the nodes accessible during a given query, which may consist of one or more trees (documents or fragments). Document order is defined in [XQuery 1.0 and XPath 2.0 Data Model], and its definition is repeated here for convenience. [Definition: The node ordering that is the reverse of document order is called reverse document order.]
Document order is a total ordering, although the relative order of some nodes is implementation-dependent. [Definition: Informally, document order is the order in which nodes appear in the XML serialization of a document.] [Definition: Document order is stable, which means that the relative order of two nodes will not change during the processing of a given query, even if this order is implementation-dependent.]
Within a tree, document order satisfies the following constraints:
The root node is the first node.
Every node occurs before all of its children and descendants.
Attribute nodes immediately follow the element node with which they are associated. The relative order of attribute nodes is stable but implementation-dependent.
The relative order of siblings is the order in which they occur in the children
property of their parent node.
Children and descendants occur before following siblings.
The relative order of nodes in distinct trees is stable but implementation-dependent, subject to the following constraint: If any node in a given tree T1 is before any node in a different tree T2, then all nodes in tree T1 are before all nodes in tree T2.
The semantics of some XQuery operators depend on a process called atomization. Atomization is applied to a value when the value is used in a context in which a sequence of atomic values is required. The result of atomization is either a sequence of atomic values or a type error. [Definition: Atomization of a sequence is defined as
the result of invoking the fn:data
function on the sequence, as defined in [XQuery 1.0 and XPath 2.0 Functions and Operators].]
The semantics of fn:data
are repeated here for convenience. The result of fn:data
is the sequence of atomic values produced by applying the following rules to each item in the input sequence:
If the item is an atomic value, it is returned.
If the item is a node, its typed value is returned.
Atomization is used in processing the following types of expressions:
Arithmetic expressions
Comparison expressions
Function calls and returns
Cast expressions
Computed element and attribute constructors.
Under certain circumstances (listed below), it is necessary to find the effective boolean value of a value. [Definition: The effective boolean value of a value is defined as the result of applying the fn:boolean
function to the value, as defined in [XQuery 1.0 and XPath 2.0 Functions and Operators].]
The semantics of fn:boolean
are repeated here for convenience. fn:boolean
returns false
if its operand is any of the following:
An empty sequence
The boolean value false
A zero-length value of type xs:string
or xdt:untypedAtomic
A numeric value that is equal to zero
The xs:double
or xs:float
value NaN
Otherwise, fn:boolean
returns true
.
The effective boolean value of a sequence is computed implicitly during processing of the following types of expressions:
Logical expressions (and
, or
)
The fn:not
function
The where
clause of a FLWOR expression
Certain types of predicates, such as a[b]
Conditional expressions (if
)
Quantified expressions (some
, every
)
Note:
Note that the definition of effective boolean value is not used when casting a value to the type xs:boolean
, for example in a cast
expression or when passing a value to a function whose expected parameter is of type xs:boolean
.
XQuery has a set of functions that provide access to input data. These functions are of particular importance because they provide a way in which an expression can reference a document or a collection of documents. The input functions are described informally here; they are defined in [XQuery 1.0 and XPath 2.0 Functions and Operators].
An expression can access input data either by calling one of the input functions or by referencing some part of the dynamic context that is initialized by the external environment, such as a variable or context item.
The input functions supported by XQuery are as follows:
The fn:doc
function takes a string containing a URI. If that URI is associated with a document in available documents, fn:doc
returns a document node whose content is the data model representation of the given document; otherwise it raises a dynamic error (see [XQuery 1.0 and XPath 2.0
Functions and Operators] for details).
The fn:collection
function with one argument takes a string containing a URI. If that URI is associated with a collection in available collections, fn:collection
returns the data model representation of that collection; otherwise it raises a dynamic error (see [XQuery 1.0 and XPath 2.0 Functions and Operators] for
details). A collection may be any sequence of nodes. For example, the expression fn:collection("http://example.org")//customer
identifies all the customer
elements that are descendants of nodes found in the collection whose URI is http://example.org
.
The fn:collection
function with zero arguments returns the default collection, an implementation-dependent sequence of nodes.
If a given input function is invoked repeatedly with arguments that resolve to the same absolute URI during the scope of a single query, each invocation must return the same node sequence.
XQuery is a strongly typed language with a type system based on [XML Schema]. The XQuery type system is formally defined in [XQuery 1.0 and XPath 2.0 Formal Semantics].
In this specification, the word "type", when used without modification, represents a type that can be expressed using the SequenceType syntax. When we refer specifically to XML Schema simple or complex types, appropriate modifiers are used to make this clear.
The in-scope type definitions in the static context are initialized with certain predefined types, including the built-in types of [XML Schema]. These built-in types are in the namespace http://www.w3.org/2001/XMLSchema
, which has the predefined namespace prefix xs
. Some examples of built-in schema types include
xs:integer
, xs:string
, and xs:date
. Element and attribute declarations in the xs
namespace are not implicitly included in the static context.
In addition, the predefined types of XQuery include the types defined in the namespace http://www.w3.org/2004/10/xpath-datatypes
, which has the predefined namespace prefix xdt
. The types in this namespace are defined in [XQuery 1.0 and XPath 2.0 Functions and Operators] and are summarized below.
[Definition: xdt:untyped
is used to denote the dynamic type of an element node that has not been validated, or has been validated in skip
mode.] No predefined types are derived from xdt:untyped
.
[Definition: xdt:untypedAtomic
is used to denote untyped atomic data, such as text that has not been assigned a more specific type.] An attribute that has been validated in skip
mode, or that has a PSVI property of xs:anySimpleType
, is represented in the Data Model by an attribute node with the type xdt:untypedAtomic
. No predefined types are derived from
xdt:untypedAtomic
.
[Definition: xdt:dayTimeDuration
is derived by restriction from xs:duration
. The lexical representation of xdt:dayTimeDuration
is restricted to contain only day, hour, minute, and second components.]
[Definition: xdt:yearMonthDuration
is derived by restriction from xs:duration
. The lexical representation of xdt:yearMonthDuration
is restricted to contain only year and month components.]
[Definition: xdt:anyAtomicType
includes all atomic values (and no values that are not atomic).] It is derived from xs:anySimpleType
, which is the base type for all simple types, including atomic, list, and union types. All specific atomic types such as xs:integer
, xs:string
, and xdt:untypedAtomic
, are derived from xdt:anyAtomicType
.
Note:
xdt:anyAtomicType
will not appear as the type of an actual value in the Data Model.
The relationships among the types in the xs
and xdt
namespaces are illustrated in Figure 2. A more complete description of the XQuery type hierarchy can be found in [XQuery 1.0 and XPath 2.0 Functions and Operators].
Figure 2: Summary of XQuery Type Hierarchy
In the data model, every node has a typed value and a string value. [Definition: The typed value of a node is a sequence of atomic values and can be extracted by applying the fn:data
function to the node.] [Definition: The string value of a node is a string and can be extracted
by applying the fn:string
function to the node.] Definitions of fn:data
and fn:string
can be found in [XQuery 1.0 and XPath 2.0 Functions and Operators].
An implementation may store both the typed value and the string value of a node, or it may store only one of these and derive the other from it as needed. In general, the string value of a node must be a valid lexical representation of the typed value of the node, but the node is not required to preserve the string representation from the original source document. For example, if the typed value of a
node is the xs:integer
value 30
, its string value might be "30
" or "0030
".
The typed value, string value, and type annotation of a node are closely related, and are defined by rules found in the following locations:
If the node was created by mapping from an Infoset or PSVI, see rules in [XQuery 1.0 and XPath 2.0 Data Model].
If the node was created by an XQuery node constructor, see rules in 3.7.1 Direct Element Constructors, 3.7.3.1 Computed Element Constructors, or 3.7.3.2 Computed Attribute Constructors.
If the node was created by a validate
expression, see rules in 3.13 Validate Expressions.
As a convenience to the reader, the relationship between typed value and string value for various kinds of nodes is summarized and illustrated by examples below.
For text and document nodes, the typed value of the node is the same as its string value, as an instance of the type xdt:untypedAtomic
. The string value of a document node is formed by concatenating the string values of all its descendant text nodes, in document order.
The typed value of a comment or processing instruction node is the same as its string value. It is an instance of the type xs:string
.
The typed value of an attribute node with the type annotation xdt:untypedAtomic
is the same as its string value, as an instance of xdt:untypedAtomic
. The typed value of an attribute node with any other type annotation is derived from its string value and type annotation using the lexical-to-value-space mapping defined in [XML Schema] Part 2 for the relevant type.
Example: A1 is an attribute having string value "3.14E-2"
and type annotation xs:double
. The typed value of A1 is the xs:double
value whose lexical representation is 3.14E-2
.
Example: A2 is an attribute with type annotation xs:IDREFS
, which is a list datatype whose item type is the atomic datatype xs:IDREF
. Its string value is "bar baz faz
". The typed value of A2 is a sequence of three atomic values ("bar
", "baz
", "faz
"), each of type xs:IDREF
. The typed value of a node is never treated as an instance of a named list type. Instead, if the type annotation of a node is a list type (such
as xs:IDREFS
), its typed value is treated as a sequence of the atomic type from which it is derived (such as xs:IDREF
).
For an element node, the relationship between typed value and string value depends on the node's type annotation, as follows:
If the type annotation is xdt:untyped
or denotes a complex type with mixed content (including xs:anyType
), then the typed value of the node is equal to its string value, as an instance of xdt:untypedAtomic
.
Example: E1 is an element node having type annotation xdt:untyped
and string value "1999-05-31
". The typed value of E1 is "1999-05-31
", as an instance of xdt:untypedAtomic
.
Example: E2 is an element node with the type annotation formula
, which is a complex type with mixed content. The content of E2 consists of the character "H
", a child element named subscript
with string value "2
", and the character "O
". The typed value of E2 is "H2O
" as an instance of xdt:untypedAtomic
.
If the type annotation denotes a simple type or a complex type with simple content, then the typed value of the node is derived from its string value and its type annotation in a way that is consistent with schema validation.
Example: E3 is an element node with the type annotation cost
, which is a complex type that has several attributes and a simple content type of xs:decimal
. The string value of E3 is "74.95
". The typed value of E3 is 74.95
, as an instance of xs:decimal
.
Example: E4 is an element node with the type annotation hatsizelist
, which is a simple type derived from the atomic type hatsize
, which in turn is derived from xs:integer
. The string value of E4 is "7 8 9
". The typed value of E4 is a sequence of three values (7
, 8
, 9
), each of type hatsize
.
Example: E5 is an element node with the type annotation my:integer-or-string
which is a union type with member types xs:integer
and xs:string
. The string value of E5 is "47
". The typed value of E5 is 47
as an xs:integer
, since xs:integer
is the member type that validated the content of E5. In general, when the type annotation of a node is a union type, the typed value of the node will be an instance of one of the
member types of the union.
Note:
If an implementation stores only the string value of a node, and the type annotation of the node is a union type, the implementation must be able to deliver the typed value of the node as an instance of the appropriate member type.
If the type annotation denotes a complex type with empty content, then the typed value of the node is the empty sequence and its string value is the zero-length string.
If the type annotation denotes a complex type with element-only content, then the typed value of the node is undefined. The fn:data
function raises a type error [err:XP0007] when applied to such a node.
Example: E6 is an element node with the type annotation weather
, which is a complex type whose content type specifies element-only
. E6 has two child elements named temperature
and precipitation
. The typed value of E6 is undefined, and the fn:data
function applied to E6 raises an error.
[Definition: When it is necessary to refer to a type in an XQuery expression, the SequenceType syntax is used. The name SequenceType suggests that this syntax is used to describe the type of an XQuery value, which is always a sequence.]
Here are some examples of SequenceTypes that might be used in XQuery expressions:
xs:date
refers to the built-in atomic Schema type named xs:date
attribute()?
refers to an optional attribute
element()
refers to any element
element(po:shipto, po:address)
refers to an element that has the name po:shipto
and has the type annotation po:address
(or a type derived from po:address
)
element(*, po:address)
refers to an element of any name that has the type annotation po:address
(or a type derived from po:address
)
element(customer)
refers to an element named customer
of any type
schema-element(customer)
refers to an element named customer
whose type annotation matches the type declared for a customer
element in the in-scope element declarations
node()*
refers to a sequence of zero or more nodes of any type
item()+
refers to a sequence of one or more nodes or atomic values
[Definition: During evaluation of an expression, it is sometimes necessary to determine whether a value with a known type "matches" an expected type, expressed in the SequenceType syntax. This process is known as SequenceType matching.] For example, an instance of
expression returns true
if the actual type of a given value matches a
given type, or false
if it does not.
QNames appearing in a SequenceType have their prefixes expanded to namespace URIs by means of the statically known namespaces and the default element/type namespace. As usual, two expanded QNames are equal if their local parts are the same and their namespace URI's are the same.
[Definition: The use of a value whose actual type is derived from the expected type is known as subtype substitution.] Subtype substitution does not change the actual type of a value. For example, if an xs:integer
value is used where an xs:decimal
value is expected, the value retains its type as xs:integer
.
The rules for SequenceType matching compare the actual type of a value with an expected type. These rules are a subset of the formal rules that match a value with an expected type defined in [XQuery 1.0 and XPath 2.0 Formal Semantics], because the Formal Semantics must be able to match a value with any XML Schema type, whereas the rules below only match values against those types expressible by the SequenceType syntax.
Some of the rules for SequenceType matching require determining whether a given type name is the same as or derived from an expected type name. The given type name may be "known" (defined in the in-scope schema definitions), or "unknown" (not defined in the in-scope schema definitions). An unknown type name might be encountered, for example, if a source document has been validated using a schema that was not imported into the static context. In this case, an implementation is allowed (but is not required) to provide an implementation-dependent mechanism for determining whether the unknown type name is derived from the expected type name. For example, an implementation might maintain a data dictionary containing information about type hierarchies.
The definition of SequenceType matching relies on a pseudo-function named derives-from(
AT, ET)
, which takes an actual simple or complex type name AT and an expected simple or complex type name ET, and either returns a boolean value or raises a type error. [err:XP0004][err:XP0006] The pseudo-function derives-from
is defined below and is defined formally in [XQuery 1.0 and XPath 2.0 Formal Semantics].
derives-from(
AT, ET)
returns true
if ET is a known type and any of the following three conditions is true:
AT is a type name found in the in-scope schema definitions, and is the same as ET or is derived by restriction or extension from ET
AT is a type name not found in the in-scope schema definitions, and an implementation-dependent mechanism is able to determine that AT is derived by restriction from ET
There exists some type name IT such that derives-from(
IT, ET)
and derives-from(
AT, IT)
are true.
derives-from(
AT, ET)
returns false
if ET is a known type and either the first and third or the second and third of the following conditions are true:
AT is a type name found in the in-scope schema definitions, and is not the same as ET, and is not derived by restriction or extension from ET
AT is a type name not found in the in-scope schema definitions, and an implementation-dependent mechanism is able to determine that AT is not derived by restriction from ET
No type name IT exists such that derives-from(
IT, ET)
and derives-from(
AT, IT)
are true.
derives-from(
AT, ET)
raises a type error [err:XP0004][err:XP0006] if:
ET is an unknown type, or
AT is an unknown type, and the implementation is not able to determine whether AT is derived by restriction from ET.
Note:
The derives-from
pseudo-function cannot be written as a real XQuery function, because types are not valid function parameters.
The rules for SequenceType matching are given below, with examples (the examples are for purposes of illustration, and do not cover all possible cases).
The SequenceType empty()
matches a value that is the empty sequence.
An ItemType with no OccurrenceIndicator matches any value that contains exactly one item if the ItemType matches that item (see 2.5.4.2 Matching an ItemType and an Item).
An ItemType with an OccurrenceIndicator matches a value if the number of items in the value matches the OccurrenceIndicator and the ItemType matches each of the items in the value.
An OccurrenceIndicator specifies the number of items in a sequence, as follows:
?
matches zero or one items
*
matches zero or more items
+
matches one or more items
As a consequence of these rules, any SequenceType whose OccurrenceIndicator is *
or ?
matches a value that is an empty sequence.
An ItemType consisting simply of a QName is interpreted as an AtomicType. An AtomicType AtomicType matches an atomic value whose actual type is AT if derives-from(
AT, AtomicType)
is true
. If a QName that is used as an AtomicType is not defined as an atomic type in the in-scope type definitions, a static error is raised. [err:XP0051]
Example: The AtomicType xs:decimal
matches the value 12.34
(a decimal literal). xs:decimal
also matches a value whose type is shoesize
, if shoesize
is an atomic type derived by restriction from xs:decimal
.
Note:
The names of non-atomic types such as xs:IDREFS
are not accepted in this context, but can often be replaced by an atomic type with an occurrence indicator, such as xs:IDREF+
.
item()
matches any single item.
Example: item()
matches the atomic value 1
or the element <a/>
.
node()
matches any node.
text()
matches any text node.
processing-instruction()
matches any processing-instruction node.
processing-instruction(
N)
matches any processing-instruction node whose name (called its "PITarget" in XML) is equal to N, where N is an NCName.
Example: processing-instruction(xml-stylesheet)
matches any processing instruction whose PITarget is xml-stylesheet
.
For backward compatibility with XPath 1.0, the PITarget of a processing instruction may also be expressed as a string literal, as in this example: processing-instruction("xml-stylesheet")
.
comment()
matches any comment node.
document-node()
matches any document node.
document-node(
E)
matches any document node that contains exactly one element node, optionally accompanied by one or more comment and processing instruction nodes, if E is an ElementTest or SchemaElementTest that matches the element node (see 2.5.4.3 Element Test and 2.5.4.4 Schema Element
Test).
Example: document-node(element(book))
matches a document node containing exactly one element node that is matched by the ElementTest element(book)
.
An ItemType that is an ElementTest, SchemaElementTest, AttributeTest, or SchemaAttributeTest matches an element or attribute node as described in the following sections.
An ElementTest is used to match an element node by its name and/or type. An ElementTest any take any of the following forms. In these forms, ElementName and TypeName may be any QNames, and need not be present in the in-scope schema definitions. Note that substitution groups do not affect the semantics of ElementTest.
element()
and element(*)
match any single element node, regardless of its name or type.
element(
ElementName)
matches any element node whose name is ElementName, regardless of its type or nilled
property.
Example: element(person)
matches any element node whose name is person
.
element(
ElementName,
TypeName)
matches an element node whose name is ElementName if derives-from(
AT, TypeName )
is true
, where AT is the type of the element node, and the nilled
property of the node is false
.
Example: element(person, surgeon)
matches a non-nilled element node whose name is person
and whose type annotation is surgeon
.
element(
ElementName, TypeName ?)
matches an element node whose name is ElementName if derives-from(
AT, TypeName)
is true
, where AT is the type of the element node. The nilled
property of the node may be either true
or false
.
Example: element(person, surgeon?)
matches a nilled or non-nilled element node whose name is person
and whose type annotation is surgeon
.
element(*,
TypeName)
matches an element node regardless of its name, if derives-from(
AT, TypeName )
is true
, where AT is the type of the element node, and the nilled
property of the node is false
.
Example: element(*, surgeon)
matches any non-nilled element node whose type annotation is surgeon
, regardless of its name.
element(*,
TypeName ?)
matches an element node regardless of its name, if derives-from(
AT, TypeName )
is true
, where AT is the type of the element node. The nilled
property of the node may be either true
or false
.
Example: element(*, surgeon?)
matches any nilled or non-nilled element node whose type annotation is surgeon
, regardless of its name.
A SchemaElementTest matches an element node against a corresponding element declaration found in the in-scope element declarations. It takes the following form:
schema-element(
ElementName)
If the ElementName specified in the SchemaElementTest is not found in the in-scope element declarations, a static error is raised. [err:XP0008]
A SchemaElementTest matches a candidate element node if all three of the following conditions are satisfied:
The name of the candidate node matches the specified ElementName or matches the name of an element in a substitution group headed by an element named ElementName.
derives-from(
AT, ET)
is true
, where AT is the type of the candidate node and ET is the type declared for element ElementName in the in-scope element declarations.
Either the nilled
property of the candidate node is false
, or the element declaration for ElementName in the in-scope element declarations is nillable
.
Example: The SchemaElementTest schema-element(customer)
matches a candidate element node if customer
is a top-level element declaration in the in-scope element declarations, the name of the candidate node is customer
or is in a substitution group headed by customer
, the type of the
candidate node is the same as or derived from the type declared for the customer
element, and either the candidate node is not nilled
or customer
is declared to be nillable
.
An AttributeTest is used to match an attribute node by its name and/or type. An AttributeTest any take any of the following forms. In these forms, AttributeName and TypeName may be any QNames, and need not be present in the in-scope schema definitions.
attribute()
and attribute(*)
match any single attribute node, regardless of its name or type.
attribute(
AttributeName)
matches any attribute node whose name is AttributeName, regardless of its type.
Example: attribute(price)
matches any attribute node whose name is price
.
attribute(
AttributeName, TypeName)
matches an attribute node whose name is AttributeName if derives-from(
AT, TypeName )
is true
, where AT is the type of the attribute node.
Example: attribute(price, currency)
matches an attribute node whose name is price
and whose type annotation is currency
.
attribute(*,
TypeName)
matches an attribute node regardless of its name, if derives-from(
AT, TypeName)
is true
, where AT is the type of the attribute node.
Example: attribute(*, currency)
matches any attribute node whose type annotation is currency
, regardless of its name.
A SchemaAttributeTest matches an attribute node against a corresponding attribute declaration found in the in-scope attribute declarations. It takes the following form:
schema-attribute(
AttributeName)
If the AttributeName specified in the SchemaAttributeTest is not found in the in-scope attribute declarations, a static error is raised. [err:XP0008]
A SchemaAttributeTest matches a candidate attribute node if both of the following conditions are satisfied:
The name of the candidate node matches the specified AttributeName.
derives-from(
AT, ET)
is true
, where AT is the type of the candidate node and ET is the type declared for attribute AttributeName in the in-scope attribute declarations.
Example: The SchemaAttributeTest schema-attribute(color)
matches a candidate attribute node if color
is a top-level attribute declaration in the in-scope attribute declarations, the name of the candidate node is color
, and the type of the candidate node is the same as or derived from the type declared for the color
attribute.
This section describes certain optional features. It is implementation-defined whether an XQuery implementation supports each of these optional features.
[Definition: If the Schema Import Feature is supported, a Prolog may contain a schema import. Definitions from the imported schema are added to the in-scope schema definitions.] If more than one schema is imported, the definitions contained in these schemas are collected into a single pool of definitions. This pool of definitions must satisfy the conditions for schema validity set out in Sections 3 and 5 of [XML Schema] Part 1. In brief, the definitions must be valid, they must be complete, and they must be unique—that is, the pool of definitions must not contain two or more definitions with the same expanded QName in the same symbol space. If any of these conditions is violated, a static error is raised.[err:XQ0012]
If an XQuery implementation that does not support the Schema Import Feature encounters a schema import, it raises a static error.[err:XQ0009] In such an implementation, the in-scope type definitions consist only of predefined type definitions, as described in C.1 Static Context Components.
[Definition: An XQuery implementation that supports the Static Typing Feature is required to detect and raise type errors during the static analysis phase.] Implementations that do not support this feature are not required to detect type errors statically; however, they must detect and raise non-type-related static errors during the static analysis phase.
[Definition: The following axes are designated as optional axes: ancestor
, ancestor-or-self
, following
, following-sibling
, preceding
, and preceding-sibling
.]
[Definition: An XQuery implementation that supports the Full Axis Feature must support all the optional axes.] For an XQuery implementation that does not support the Full Axis Feature, the set of optional axes that are supported is implementation-defined. If an implementation encounters a reference to an optional axis that it does not support, it must raise a static error. [err:XQ0010]
Note that XQuery does not recognize the namespace
axis (defined by XPath 1.0 and deprecated by XPath 2.0).
[Definition: An XQuery implementation that does not support the Module Feature raises a static error [err:XQ0016] if it encounters a module declaration or a module import.] Since a module declaration is required in a library module, the Module Feature is required in order to create a library module. In the absence of this feature, each query consists of a single main module.
[Definition: An XQuery implementation may choose to support either [XML 1.0] and [XML Names], or alternatively, [XML 1.1] and [XML Names 1.1]. An implementation that supports the latter pair of specifications is said to support the XML and Names 1.1 Feature.] This feature affects the space of valid names and certain aspects of serialization, as described elsewhere in this document.
[Definition: A pragma may be used to provide additional information to an XQuery implementation.] Support for a pragma does not negate the requirement to support normal XQuery functionality in the absence of the pragma.
[147] | Pragma |
::= | "(::" S? "pragma" S QName (S ExtensionContents)? "::)" |
[149] | ExtensionContents |
::= | (Char* - (Char* '::)' Char*)) |
The QName of a Pragma must contain an explicit namespace prefix. Within a Pragma, the character content may consist of any sequence of characters that does not include the sequence "::)
". Pragmas may be used anywhere that ignorable whitespace is allowed. A pragma is identified by its QName.
If an implementation does not support a pragma, then that pragma shall be ignored. If an implementation does support a pragma and the implementation determines that the character content is invalid, then a static error is raised.[err:XQ0013] Otherwise, the effect of the pragma on the result of the Query is implementation-defined.
The following example shows how a pragma might be used:
declare namespace exq = "http://example.org/XQueryImplementation"; (:: pragma exq:timeout 1000 ::) fn:count($bib/book/author)
An implementation that supports the exq:timeout
pragma might raise a dynamic error if it is unable to count the authors within 1000 seconds. An implementation that does not support this pragma would execute as long as necessary to count the authors.
[Definition: An implementation may extend XQuery functionality by supporting must-understand extensions.]
[148] | MUExtension |
::= | "(::" S? "extension" S QName (S ExtensionContents)? "::)" |
[149] | ExtensionContents |
::= | (Char* - (Char* '::)' Char*)) |
A must-understand extension is identified by its QName, which must contain an explicit namespace prefix. The character content may consist of any sequence of characters that does not include the sequence "::)
". A must-understand extension may be used anywhere that ignorable whitespace is allowed.
If an implementation does not support a must-understand extension, then a static error is raised.[err:XQ0014] If an implementation does support a must-understand extension and the implementation determines that the character content is invalid, then a static error is raised. Otherwise, the effect of the must-understand extension on the result of the Query is implementation-defined.
The following example shows how a must-understand extension might be used:
declare namespace exq = "http://example.org/XQueryImplementation"; for $e in fn:doc("denver.xml")/staff/employee order by $e/lastname (:: extension exq:RightToLeft ::) return $e
An implementation that supports the exq:RightToLeft
extension might order the last names by examining characters from right to left instead of from left to right. An implementation that does not support this extension would raise a static error.
[Definition: An XQuery Flagger is a facility that is provided by an implementation that is able to identify queries that contain must-understand extensions. If an implementation supports must-understand extensions, then an XQuery Flagger must be provided.] The XQuery Flagger is disabled by default; the mechanism by which the XQuery Flagger is enabled is implementation-defined. If the XQuery Flagger is enabled, a static error [err:XQ0015] is raised if the query contains a must-understand extension.
An XQuery Flagger is provided to assist programmers in producing queries that are portable among multiple conforming XQuery implementations.
The following example illustrates how an XQuery Flagger might be used:
xquery RightToLeft.xquery -Flagger=on
If RightToLeft.xquery
contains a must-understand extension such as exq:RightToLeft
, then this XQuery invocation will result in a static error. If the XQuery Flagger was not enabled and the implementation supports exq:RightToLeft
, then this query might execute without error.
In some cases, the static typing rules defined in [XQuery 1.0 and XPath 2.0 Formal Semantics] are not very precise (see, for instance, the type inference rules for the ancestor axes—parent, ancestor, and ancestor-or-self—and for the function fn:root
). Some implementations may wish to support more precise static typing rules.
A conforming implementation may provide a static typing extension. [Definition: A static typing extension is a type inference rule that infers a more precise static type than that inferred by the type inference rules in [XQuery 1.0 and XPath 2.0 Formal Semantics].] That is, given an expression E, and its static type T inferred by the type inference rules in [XQuery 1.0 and XPath 2.0 Formal Semantics], an implementation may infer a static type T1 for E such that T1 is a subtype of T (that is, all instances of T1 are also instances of T).
Note:
It is not recommended for a static typing extension to change the static type behavior of the treat
expression, since static type behavior is central to the semantics of this expression.
[Definition: An XQuery Static Flagger is a facility that is able to identify queries that require a static typing extension.] If an implementation supports static typing extensions, then it must also provide an XQuery Static Flagger. The XQuery Static Flagger is disabled by default; the mechanism by which it is enabled is implementation-defined. When enabled, the XQuery Static Flagger must raise a static error during the static analysis phase wherever a type error is called for by the rules in [XQuery 1.0 and XPath 2.0 Formal Semantics]. The purpose of an XQuery Static Flagger is to assist programmers in producing queries that are portable among multiple conforming XQuery implementations.
The following example illustrates how an XQuery Static Flagger might be used:
xquery abc.xquery -StaticFlagger=on
If abc.xquery
contains a type error according to the static semantic rules in [XQuery 1.0 and XPath 2.0 Formal Semantics], then this XQuery invocation will result in a static error. If the XQuery Static Flagger was not enabled and the implementation supports a static typing extension, then this query might execute without
error.
[150] | Comment |
::= | "(:" (CommentContents | Comment)* ":)" |
[151] | CommentContents |
::= | (Char+ - (Char* ':)' Char*)) |
Comments may be used to provide informative annotation for a query, either in the Prolog or in the Query Body. Comments are lexical constructs only, and do not affect query processing.
Comments are strings, delimited by the symbols (:
and :)
. Comments may be nested.
A comment may be used anywhere ignorable whitespace is allowed. Within a comment, pragmas and must-understand extensions are treated as nested comments. For examples of how comments interact with pragmas and must-understand extensions, see A.2.3 Comments, Pragmas and Extensions.
The following is an example of a comment:
(: Houston, we have a problem :)
This section discusses each of the basic kinds of expression. Each kind of expression has a name such as PathExpr
, which is introduced on the left side of the grammar production that defines the expression. Since XQuery is a composable language, each kind of expression is defined in terms of other expressions whose operators have a higher precedence. In this way, the precedence of operators is represented explicitly in the grammar.
The order in which expressions are discussed in this document does not reflect the order of operator precedence. In general, this document introduces the simplest kinds of expressions first, followed by more complex expressions. For the complete grammar, see Appendix [A XQuery Grammar].
[28] | Expr |
::= | ExprSingle ("," ExprSingle)* |
[29] | ExprSingle |
::= | FLWORExpr |
A query may consist of one or more modules, as described in 4 Modules and Prologs. If a query is executable, one of its modules has a Query Body containing an expression whose value is the result of the query. An expression is represented in the XQuery grammar by the symbol Expr.
The XQuery operator that has lowest precedence is the comma operator, which is used to combine two operands to form a sequence. As shown in the grammar, a general expression (Expr) can consist of two operands (ExprSingle) separated by a comma. The name ExprSingle denotes an expression that does not contain a top-level comma operator (despite its name, an ExprSingle may evaluate to a sequence containing more than one item.)
The symbol ExprSingle is used in various places in the grammar where an expression is not allowed to contain a top-level comma. For example, each of the arguments of a function call must be an ExprSingle, because commas are used to separate the arguments of a function call.
After the comma, the expressions that have next lowest precedence are FLWORExpr, QuantifiedExpr, TypeswitchExpr, IfExpr, and OrExpr. Each of these expressions is described in a separate section of this document.
[Definition: Primary expressions are the basic primitives of the language. They include literals, variable references, context item expressions, constructors, and function calls. A primary expression may also be created by enclosing any expression in parentheses, which is sometimes helpful in controlling the precedence of operators.] Constructors are described in 3.7 Constructors.
[77] | PrimaryExpr |
::= | Literal | VarRef | ParenthesizedExpr | ContextItemExpr | FunctionCall | Constructor | OrderedExpr | UnorderedExpr |
[Definition: A literal is a direct syntactic representation of an atomic value.] XQuery supports two kinds of literals: numeric literals and string literals.
[78] | Literal |
::= | NumericLiteral | StringLiteral |
[79] | NumericLiteral |
::= | IntegerLiteral | DecimalLiteral | DoubleLiteral |
[132] | IntegerLiteral |
::= | Digits |
[133] | DecimalLiteral |
::= | ("." Digits) | (Digits "." [0-9]*) |
[134] | DoubleLiteral |
::= | (("." Digits) | (Digits ("." [0-9]*)?)) [eE] [+-]? Digits |
[135] | StringLiteral |
::= | ('"' (PredefinedEntityRef | CharRef | ('"' '"') | [^"&])* '"') | ("'" (PredefinedEntityRef | CharRef | ("'" "'") | [^'&])* "'") |
[140] | PredefinedEntityRef |
::= | "&" ("lt" | "gt" | "amp" | "quot" | "apos") ";" |
[139] | Digits |
::= | [0-9]+ |
The value of a numeric literal containing no ".
" and no e
or E
character is an atomic value of type xs:integer
. The value of a numeric literal containing ".
" but no e
or E
character is an atomic value of type xs:decimal
. The value of a numeric literal containing an e
or E
character is an atomic value of type xs:double
. Values of numeric literals are
interpreted according to the rules in [XML Schema].
The value of a string literal is an atomic value whose type is xs:string
and whose value is the string denoted by the characters between the delimiting apostrophes or quotation marks. If the literal is delimited by apostrophes, two adjacent apostrophes within the literal are interpreted as a single apostrophe. Similarly, if the literal is delimited by quotation marks, two adjacent quotation marks within the literal are interpreted as one quotation mark.
Within a string literal, line endings are normalized according to the rules for "End-of-Line Handling" in Section 2.11 of [XML 1.0] (if the XML and Names 1.1 Feature is supported, the rules in Section 2.11 of [XML 1.1] apply).
A string literal may contain a predefined entity reference, which is a short sequence of characters, beginning with an ampersand, that represents a single character that might otherwise have syntactic significance. Each predefined entity reference is replaced by the character it represents when the string literal is processed. The predefined entity references recognized by XQuery are as follows:
Entity Reference | Character Represented |
< |
< |
> |
> |
& |
& |
" |
" |
' |
' |
A string literal may also contain a character reference, which is an XML-style reference to a [Unicode] character, identified by its decimal or hexadecimal code point. For example, the Euro symbol (€) can be represented by the character reference €
. Character references are defined in Section 4.1 of [XML 1.0] (if the XML and Names 1.1 Feature is
supported, the definition in Section 4.1 of [XML 1.1] applies).
Here are some examples of literal expressions:
"12.5"
denotes the string containing the characters '1', '2', '.', and '5'.
12
denotes the integer value twelve.
12.5
denotes the decimal value twelve and one half.
125E2
denotes the double value twelve thousand, five hundred.
"He said, ""I don't like it."""
denotes a string containing two quotation marks and one apostrophe.
"Ben & Jerry's"
denotes the string "Ben & Jerry's
".
"€99.50"
denotes the string "€99.50
".
The boolean values true
and false
can be represented by calls to the built-in functions fn:true()
and fn:false()
, respectively.
Values of other atomic types can be constructed by calling the constructor for the given type. The constructors for XML Schema built-in types are defined in [XQuery 1.0 and XPath 2.0 Functions and Operators]. In general, the name of a constructor function for a given type is the same as the name of the type (including its namespace). For example:
xs:integer("12")
returns the integer value twelve.
xs:date("2001-08-25")
returns an item whose type is xs:date
and whose value represents the date 25th August 2001.
xdt:dayTimeDuration("PT5H")
returns an item whose type is xdt:dayTimeDuration
and whose value represents a duration of five hours.
Constructor functions can also be used to create special values that have no literal representation, as in the following examples:
xs:float("NaN")
returns the special floating-point value, "Not a Number."
xs:double("INF")
returns the special double-precision value, "positive infinity."
It is also possible to construct values of various types by using a cast
expression. For example:
9 cast as hatsize
returns the atomic value 9
whose type is hatsize
.
[80] | VarRef |
::= | "$" VarName |
[137] | VarName |
::= | QName |
[Definition: A variable reference is a QName preceded by a $-sign.] Two variable references are equivalent if their local names are the same and their namespace prefixes are bound to the same namespace URI in the statically known namespaces. An unprefixed variable reference is in no namespace.
Every variable reference must match a name in the in-scope variables, which include variables from the following sources:
A variable may be declared in a Prolog, in the current module or an imported module. See 4 Modules and Prologs for a discussion of modules and Prologs.
A variable may be added to the in-scope variables by the host language environment.
A variable may be bound by an XQuery expression. The kinds of expressions that can bind variables are FLWOR expressions (3.8 FLWOR Expressions), quantified expressions (3.11 Quantified Expressions), and typeswitch
expressions (3.12.2 Typeswitch). Function calls also bind values to the formal parameters of functions before
executing the function body.
Every variable binding has a static scope. The scope defines where references to the variable can validly occur. It is a static error [err:XP0008] to reference a variable that is not in scope. If a variable is bound in the static context for an expression, that variable is in scope for the entire expression.
If a variable reference matches two or more variable bindings that are in scope, then the reference is taken as referring to the inner binding, that is, the one whose scope is smaller. At evaluation time, the value of a variable reference is the value of the expression to which the relevant variable is bound. The scope of a variable binding is defined separately for each kind of expression that can bind variables.
[81] | ParenthesizedExpr |
::= | "(" Expr? ")" |
Parentheses may be used to enforce a particular evaluation order in expressions that contain multiple operators. For example, the expression (2 + 4) * 5
evaluates to thirty, since the parenthesized expression (2 + 4)
is evaluated first and its result is multiplied by five. Without parentheses, the expression 2 + 4 * 5
evaluates to twenty-two, because the multiplication operator has higher precedence than the addition operator.
Empty parentheses are used to denote an empty sequence, as described in 3.3.1 Constructing Sequences.
[82] | ContextItemExpr |
::= | "." |
A context item expression evaluates to the context item, which may be either a node (as in the expression fn:doc("bib.xml")/books/book[fn:count(./author)>1]
) or an atomic value (as in the expression (1 to 100)[. mod 5 eq 0]
).
If the context item is undefined, a context item expression raises a dynamic error.[err:XP0002]
[Definition: The built-in functions supported by XQuery are defined in [XQuery 1.0 and XPath 2.0 Functions and Operators].] Additional functions may be declared in a Prolog, imported from a library module, or provided by the external environment as part of the static context.
[85] | FunctionCall |
::= | QName "(" (ExprSingle ("," ExprSingle)*)? ")" |
A function call consists of a QName followed by a parenthesized list of zero or more expressions, called arguments. If the QName in the function call has no namespace prefix, it is considered to be in the default function namespace.
If the expanded QName and number of arguments in a function call do not match the name and arity of a function signature in the static context, a static error is raised.[err:XP0017]
A function call is evaluated as follows:
Argument expressions are evaluated, producing argument values. The order of argument evaluation is implementation-dependent and a function need not evaluate an argument if the function can evaluate its body without evaluating that argument.
Each argument value is converted by applying the function conversion rules listed below.
If the function is a built-in function, it is evaluated using the converted argument values. The result is either an instance of the function's declared return type or a dynamic error. Errors raised by built-in functions are defined in [XQuery 1.0 and XPath 2.0 Functions and Operators].
If the function is a user-declared function, the converted argument values are bound to the formal parameters of the function, and the function body is evaluated. The value returned by the function body is then converted to the declared return type of the function by applying the function conversion rules.
When a converted argument value is bound to a function parameter, the argument value retains its most specific dynamic type, even though this type may be derived from the type of the formal parameter. For example, a function with a parameter $p
of type xs:decimal
can be invoked with an argument of type xs:integer
, which is derived from xs:decimal
. During the processing of this function invocation, the
dynamic type of $p
inside the body of the function is considered to be xs:integer
. Similarly, the value returned by a function retains its most specific type, which may be derived from the declared return type of the function. For example, a function that has a declared return type of xs:decimal
may in fact return a value of dynamic type xs:integer
.
During execution of a function body, the static context and dynamic context for expression evaluation are defined by the module in which the function is declared, which is not necessarily the same as the module in which the function is called. As an example of this rule, a function does not inherit a focus (context item, context position, and context size) from the calling environment. During evaluation of a function body, the focus is undefined, except where it is defined by the action of some expression inside the function body.
The function conversion rules are used to convert an argument value or a return value to its expected type; that is, to the declared type of the function parameter or return. The expected type is expressed as a SequenceType. The function conversion rules are applied to a given value as follows:
If the expected type is a sequence of an atomic type (possibly with an occurrence indicator *
, +
, or ?
), the following conversions are applied:
Atomization is applied to the given value, resulting in a sequence of atomic values.
Each item in the atomic sequence that is of type xdt:untypedAtomic
is cast to the expected atomic type. For built-in functions where the expected type is specified as numeric
, arguments of type xdt:untypedAtomic
are cast to xs:double
.
For each numeric item in the atomic sequence that can be promoted to the expected atomic type using numeric type promotion as described in B.1 Numeric Type Promotion, the promotion is done.
If, after the above conversions, the resulting value does not match the expected type according to the rules for SequenceType Matching, a type error is raised. [err:XP0004][err:XP0006] If the function call takes place in a module other than the module in which the function is defined, this rule must be satisfied in both the module where the function is called and the module where the function is defined (the test is repeated because the two modules may have different in-scope schema definitions.) Note that the rules for SequenceType Matching permit a value of a derived type to be substituted for a value of its base type.
Since the arguments of a function call are separated by commas, any argument expression that contains a top-level comma operator must be enclosed in parentheses. Here are some illustrative examples of function calls:
my:three-argument-function(1, 2, 3)
denotes a function call with three arguments.
my:two-argument-function((1, 2), 3)
denotes a function call with two arguments, the first of which is a sequence of two values.
my:two-argument-function(1, ())
denotes a function call with two arguments, the second of which is an empty sequence.
my:one-argument-function((1, 2, 3))
denotes a function call with one argument that is a sequence of three values.
my:one-argument-function(( ))
denotes a function call with one argument that is an empty sequence.
my:zero-argument-function( )
denotes a function call with zero arguments.
A path expression can be used to locate nodes within trees.
[61] | PathExpr |
::= | ("/" RelativePathExpr?) |
[62] | RelativePathExpr |
::= | StepExpr (("/" | "//") StepExpr)* |
A path expression consists of a series of one or more steps, separated by "/
" or "//
", and optionally beginning with "/
" or "//
". An initial "/
" or "//
" is an abbreviation for one or more initial steps that are implicitly added to the beginning of the path expression, as described below.
A path expression consisting of a single step is evaluated as described in 3.2.1 Steps.
A "/
" at the beginning of a path expression is an abbreviation for the initial step fn:root(self::node()) treat as document-node()
(this is true even if the "/
" is the entire path expression). The effect of this initial step is to begin the path at the root node of the tree that contains the context node. If the context item is not a node, a type error is raised.[err:XP0020]
At evaluation time, if the root node above the context node is not a document node, a dynamic error is raised.[err:XP0050]
A "//
" at the beginning of a path expression is an abbreviation for the initial steps fn:root(self::node()) treat as document-node()/descendant-or-self::node()/
. The effect of these initial steps is to establish an initial node sequence that contains the root of the tree in which the context node is found, plus all nodes descended from this root. This node sequence is used as the input to subsequent steps in the path expression. If the context item is not a node, a type error is raised.[err:XP0020] At evaluation time, if the root node above the context node is not a document node, a dynamic error is raised.[err:XP0050]
Note:
The descendants of a node do not include attribute nodes.
Each non-initial occurrence of "//
" in a path expression is expanded as described in 3.2.4 Abbreviated Syntax, leaving a sequence of steps separated by "/
". This sequence of steps is then evaluated from left to right. Each operation E1/E2
is evaluated as follows: Expression E1
is evaluated, and if the result is not a (possibly empty) sequence of nodes, a type error is
raised.[err:XP0019] Each node resulting from the evaluation of E1
then serves in turn to provide an inner focus for an evaluation of E2
, as described in 2.1.2 Dynamic Context. The sequences resulting from all the evaluations of E2
are combined as follows:
If every evaluation of E2
returns a (possibly empty) sequence of nodes, these sequences are combined, and duplicate nodes are eliminated based on node identity. If ordering mode is ordered
, the resulting node sequence is returned in document order; otherwise it is returned in implementation-dependent order.
If every evaluation of E2
returns a (possibly empty) sequence of atomic values, these sequences are concatenated, in order, and returned.
Otherwise (that is, if the multiple evaluations of E2
return at least one node and at least one atomic value), a type error is raised.[err:XP0018].
Note:
Since each step in a path provides context nodes for the following step, in effect, only the last step in a path is allowed to return a sequence of atomic values.
As an example of a path expression, child::div1/child::para
selects the para
element children of the div1
element children of the context node, or, in other words, the para
element grandchildren of the context node that have div1
parents.
Note:
The "/
" character can be used either as an individual token or as part of a pattern such as "/*
". This can cause parsing difficulties when "/
" appears on the left hand side of an operator. For example, "/*
" and "/ *
" are valid path expressions containing wildcards, but "/*5
" and "/ * 5
" raise parsing errors. Parentheses must be used when "/
" is used as the first operand of an
operator, as in "(/) * 5
". Similarly, "4 + / * 5
" raises a parsing error, but "4 + (/) * 5
" is a valid expression. The expression 4 + /
" is also valid, because /
does not occur on the left hand side of the operator.
[63] | StepExpr |
::= | AxisStep | FilterExpr |
[64] | AxisStep |
::= | (ForwardStep | ReverseStep) PredicateList |
[65] | ForwardStep |
::= | (ForwardAxis NodeTest) | AbbrevForwardStep |
[68] | ReverseStep |
::= | (ReverseAxis NodeTest) | AbbrevReverseStep |
[75] | PredicateList |
::= | Predicate* |
A step generates a sequence of items and then filters the sequence by zero or more predicates. The value of the step consists of those items that satisfy the predicates. A step may be either an axis step or a filter expression. Filter expressions are described in 3.3.2 Filter Expressions.
The result of an axis step is always a sequence of zero or more nodes, and these nodes are always returned in document order. An axis step may be either a forward step or a reverse step, followed by zero or more predicates. An axis step might be thought of as beginning at the context node and navigating to those nodes that are reachable from the context node via a specified axis. Such a step has two parts: an axis, which defines the "direction of movement" for the step, and a node test, which selects nodes based on their kind, name, and/or type. If the context item is not a node, a type error is raised.[err:XP0020]
In the abbreviated syntax for a step, the axis can be omitted and other shorthand notations can be used as described in 3.2.4 Abbreviated Syntax.
The unabbreviated syntax for an axis step consists of the axis name and node test separated by a double colon. The result of the step consists of the nodes reachable from the context node via the specified axis that have the node kind, name, and/or type specified by the node test. For example, the step child::para
selects the para
element children of the context node: child
is the name of the axis, and para
is the name of the element nodes to be
selected on this axis. The available axes are described in 3.2.1.1 Axes. The available node tests are described in 3.2.1.2 Node Tests. Examples of steps are provided in 3.2.3 Unabbreviated Syntax and 3.2.4 Abbreviated Syntax.
[66] | ForwardAxis |
::= | ("child" "::") |
[69] | ReverseAxis |
::= | ("parent" "::") |
XQuery supports the following axes (subject to limitations as described in 2.6.3 Full Axis Feature):
The child
axis contains the children of the context node, which are the nodes returned by the dm:children
accessor in [XQuery 1.0 and XPath 2.0 Data Model].
Note:
Only document nodes and element nodes have children. If the context node is any other kind of node, or if the context node is an empty document or element node, then the child axis is an empty sequence. The children of a document node or element node may be element, processing instruction, comment, or text nodes. Attribute and document nodes can never appear as children.
the descendant
axis is defined as the transitive closure of the child axis; it contains the descendants of the context node (the children, the children of the children, and so on)
the parent
axis contains the sequence returned by the dm:parent
accessor in [XQuery 1.0 and XPath 2.0 Data Model], which returns the parent of the context node, or an empty sequence if the context node has no parent
Note:
An attribute node may have an element node as its parent, even though the attribute node is not a child of the element node.
the ancestor
axis is defined as the transitive closure of the parent axis; it contains the ancestors of the context node (the parent, the parent of the parent, and so on)
Note:
The ancestor axis includes the root node of the tree in which the context node is found, unless the context node is the root node.
the following-sibling
axis contains the context node's following siblings, those children of the context node's parent that occur after the context node in document order; if the context node is an attribute node, the following-sibling
axis is empty
the preceding-sibling
axis contains the context node's preceding siblings, those children of the context node's parent that occur before the context node in document order; if the context node is an attribute node, the preceding-sibling
axis is empty
the following
axis contains all nodes that are descendants of the root of the tree in which the context node is found, are not descendants of the context node, and occur after the context node in document order
the preceding
axis contains all nodes that are descendants of the root of the tree in which the context node is found, are not ancestors of the context node, and occur before the context node in document order
the attribute
axis contains the attributes of the context node, which are the nodes returned by the dm:attributes
accessor in [XQuery 1.0 and XPath 2.0 Data Model]; the axis will be empty unless the context node is an element
the self
axis contains just the context node itself
the descendant-or-self
axis contains the context node and the descendants of the context node
the ancestor-or-self
axis contains the context node and the ancestors of the context node; thus, the ancestor-or-self axis will always include the root node
Axes can be categorized as forward axes and reverse axes. An axis that only ever contains the context node or nodes that are after the context node in document order is a forward axis. An axis that only ever contains the context node or nodes that are before the context node in document order is a reverse axis.
The parent
, ancestor
, ancestor-or-self
, preceding
, and preceding-sibling
axes are reverse axes; all other axes are forward axes. The ancestor
, descendant
, following
, preceding
and self
axes partition a document (ignoring attribute nodes): they do not overlap and together they contain all the nodes in the document.
In a sequence of nodes selected by an axis step, each node is assigned a context position that corresponds to its position in the sequence. If the axis is a forward axis, context positions are assigned to the nodes in document order, starting with 1. If the axis is a reverse axis, context positions are assigned to the nodes in reverse document order, starting with 1. This makes it possible to select a node from the sequence by specifying its position.
Note:
One example of an expression that uses the context position is a numeric predicate. The expression child::para[1]
selects the first para
element that is a child of the context node.
[Definition: A node test is a condition that must be true for each node selected by a step.] The condition may be based on the kind of the node (element, attribute, text, document, comment, or processing instruction), the name of the node, or (in the case of element, attribute, and document nodes), the type of the node.
[71] | NodeTest |
::= | KindTest | NameTest |
[72] | NameTest |
::= | QName | Wildcard |
[73] | Wildcard |
::= | "*" |
[Definition: Every axis has a principal node kind. If an axis can contain elements, then the principal node kind is element; otherwise, it is the kind of nodes that the axis can contain.] Thus:
For the attribute axis, the principal node kind is attribute.
For all other axes, the principal node kind is element.
[Definition: A node test that consists only of a QName or a Wildcard is called a name test.] A name test is true if and only if the kind of the node is the principal node kind and the expanded QName of the node is equal (on a codepoint basis) to the expanded QName specified by the name test. For example, child::para
selects the para
element children of the context node; if the context node has no para
children, it selects an empty set of nodes. attribute::abc:href
selects the attribute of the context node with the QName abc:href
; if the context node has no such attribute, it selects an empty set of nodes.
A QName in a name test is resolved into an expanded QName using the statically known namespaces in the expression context. It is a static error [err:XP0008] if the QName has a prefix that does not correspond to any statically known namespace. An unprefixed QName, when used as a name test on an axis whose principal node kind is element, has the namespace URI of the default element/type namespace in the expression context; otherwise, it has no namespace URI.
A name test is not satisfied by an element node whose name does not match the expanded QName of the name test, even if it is in a substitution group whose head is the named element.
A node test *
is true for any node of the principal node kind. For example, child::*
will select all element children of the context node, and attribute::*
will select all attributes of the context node.
A node test can have the form NCName:*
. In this case, the prefix is expanded in the same way as with a QName, using the statically known namespaces in the static context. If the prefix is not found in the statically known namespaces, a static error is raised.[err:XP0008]
The node test is true for any node of the principal node kind whose expanded QName has the namespace URI to which the prefix is bound, regardless of the local part of the name.
A node test can also have the form *:NCName
. In this case, the node test is true for any node of the principal node kind whose local name matches the given NCName, regardless of its namespace or lack of a namespace.
[Definition: An alternative form of a node test called a kind test can select nodes based on their kind, name, and type annotation.] The syntax and semantics of a kind test are described in 2.5.3 SequenceType Syntax and 2.5.4 SequenceType Matching. When a kind test is used in a node test, only those nodes on the designated axis that match the kind test are selected. Shown below are several examples of kind tests that might be used in path expressions:
node()
matches any node.
text()
matches any text node.
comment()
matches any comment node.
element()
matches any element node.
schema-element(person)
matches any element node whose name is person
(or is in the substitution group headed by person
), and whose type annotation is the same as (or is derived from) the declared type of the person
element in the in-scope element declarations.
element(person)
matches any element node whose name is person
, without any restriction on type.
element(person, surgeon)
matches any non-nilled element node whose name is person
, and whose type annotation is surgeon
or is derived from surgeon
.
element(*, surgeon)
matches any non-nilled element node whose type annotation is surgeon
, regardless of its name.
attribute()
matches any attribute node.
attribute(price)
matches any attribute whose name is price
, regardless of its type.
attribute(*, xs:decimal)
matches any attribute whose type annotation is xs:decimal
, regardless of its name.
document-node()
matches any document node.
document-node(element(book))
matches any document node whose content consists of a single element node that satisfies the kind test element(book)
, interleaved with zero or more comments and processing instructions.
[76] | Predicate |
::= | "[" Expr "]" |
[Definition: A predicate consists of an expression, called a predicate expression, enclosed in square brackets. A predicate serves to filter a sequence, retaining some items and discarding others.] For each item in the sequence to be filtered, the predicate expression is evaluated using an inner focus derived from that item, as described in 2.1.2 Dynamic Context. The result of the
predicate expression is coerced to a xs:boolean
value, called the predicate truth value, as described below. Those items for which the predicate truth value is true
are retained, and those for which the predicate truth value is false
are discarded.
The predicate truth value is derived by applying the following rules, in order:
If the value of the predicate expression is an atomic value of a numeric type, the predicate truth value is true
if the value of the predicate expression is equal (by the eq
operator) to the context position, and is false
otherwise. [Definition: A predicate whose predicate expression returns a numeric type is called a numeric
predicate.]
Otherwise, the predicate truth value is the effective boolean value of the predicate expression.
Here are some examples of axis steps that contain predicates:
This example selects the second chapter
element that is a child of the context node:
child::chapter[2]
This example selects all the descendants of the context node that are elements named "toy"
and whose color
attribute has the value "red"
:
descendant::toy[attribute::color = "red"]
This example selects all the employee
children of the context node that have both a secretary
child element and an assistant
child element:
child::employee[secretary][assistant]
When using predicates with a sequence of nodes selected using a reverse axis, it is important to remember that the the context positions for such a sequence are assigned in reverse document order. For example, preceding::foo[1]
returns the first qualifying foo
element in reverse document
order, because the predicate is part of an axis step using a reverse axis. By contrast, (preceding::foo)[1]
returns the first qualifying foo
element in document order, because the parentheses cause (preceding::foo)
to be parsed as a primary expression in which context positions are assigned in document order. Similarly,
ancestor::*[1]
returns the nearest ancestor element, because the ancestor
axis is a reverse axis, whereas (ancestor::*)[1]
returns the root element (first ancestor in document order).
This section provides a number of examples of path expressions in which the axis is explicitly specified in each step. The syntax used in these examples is called the unabbreviated syntax. In many common cases, it is possible to write path expressions more concisely using an abbreviated syntax, as explained in 3.2.4 Abbreviated Syntax.
child::para
selects the para
element children of the context node
child::*
selects all element children of the context node
child::text()
selects all text node children of the context node
child::node()
selects all the children of the context node, whatever their node type. Note that no attribute nodes are returned, because attributes are not children.
attribute::name
selects the name
attribute of the context node
attribute::*
selects all the attributes of the context node
parent::node()
selects the parent of the context node. If the context node is an attribute node, this expression returns the element node (if any) to which the attribute node is attached.
descendant::para
selects the para
element descendants of the context node
ancestor::div
selects all div
ancestors of the context node
ancestor-or-self::div
selects the div
ancestors of the context node and, if the context node is a div
element, the context node as well
descendant-or-self::para
selects the para
element descendants of the context node and, if the context node is a para
element, the context node as well
self::para
selects the context node if it is a para
element, and otherwise returns an empty sequence
child::chapter/descendant::para
selects the para
element descendants of the chapter
element children of the context node
child::*/child::para
selects all para
grandchildren of the context node
/
selects the root of the tree that contains the context node, but raises a dynamic error if this root is not a document node
/descendant::para
selects all the para
elements in the same document as the context node
/descendant::list/child::member
selects all the member
elements that have a list
parent and that are in the same document as the context node
child::para[fn:position() = 1]
selects the first para
child of the context node
child::para[fn:position() = fn:last()]
selects the last para
child of the context node
child::para[fn:position() = fn:last()-1]
selects the last but one para
child of the context node
child::para[fn:position() > 1]
selects all the para
children of the context node other than the first para
child of the context node
following-sibling::chapter[fn:position() = 1]
selects the next chapter
sibling of the context node
preceding-sibling::chapter[fn:position() = 1]
selects the previous chapter
sibling of the context node
/descendant::figure[fn:position() = 42]
selects the forty-second figure
element in the document containing the context node
/child::book/child::chapter[fn:position() = 5]/child::section[fn:position() = 2]
selects the second section
of the fifth chapter
of the book
whose parent is the document node that contains the context node
child::para[attribute::type="warning"]
selects all para
children of the context node that have a type
attribute with value warning
child::para[attribute::type='warning'][fn:position() = 5]
selects the fifth para
child of the context node that has a type
attribute with value warning
child::para[fn:position() = 5][attribute::type="warning"]
selects the fifth para
child of the context node if that child has a type
attribute with value warning
child::chapter[child::title='Introduction']
selects the chapter
children of the context node that have one or more title
children whose typed value is equal to the string Introduction
child::chapter[child::title]
selects the chapter
children of the context node that have one or more title
children
child::*[self::chapter or self::appendix]
selects the chapter
and appendix
children of the context node
child::*[self::chapter or self::appendix][fn:position() = fn:last()]
selects the last chapter
or appendix
child of the context node
[67] | AbbrevForwardStep |
::= | "@"? NodeTest |
[70] | AbbrevReverseStep |
::= | ".." |
The abbreviated syntax permits the following abbreviations:
The attribute axis attribute::
can be abbreviated by @
. For example, a path expression para[@type="warning"]
is short for child::para[attribute::type="warning"]
and so selects para
children with a type
attribute with value equal to warning
.
If the axis name is omitted from an axis step, the default axis is child
unless the axis step contains an AttributeTest; in that case, the default axis is attribute
. For example, the path expression section/para
is an abbreviation for child::section/child::para
, and the path expression section/@id
is an abbreviation for child::section/attribute::id
. Similarly,
section/attribute(id)
is an abbreviation for child::section/attribute::attribute(id)
. Note that the latter expression contains both an axis specification and a node test.
Each non-initial occurrence of //
is effectively replaced by /descendant-or-self::node()/
during processing of a path expression. For example, div1//para
is short for child::div1/descendant-or-self::node()/child::para
and so will select all para
descendants of div1
children.
Note:
The path expression //para[1]
does not mean the same as the path expression /descendant::para[1]
. The latter selects the first descendant para
element; the former selects all descendant para
elements that are the first para
children of their respective parents.
A step consisting of ..
is short for parent::node()
. For example, ../title
is short for parent::node()/child::title
and so will select the title
children of the parent of the context node.
Note:
The expression .
, known as a context item expression, is a primary expression, and is described in 3.1.4 Context Item Expression.
Here are some examples of path expressions that use the abbreviated syntax:
para
selects the para
element children of the context node
*
selects all element children of the context node
text()
selects all text node children of the context node
@name
selects the name
attribute of the context node
@*
selects all the attributes of the context node
para[1]
selects the first para
child of the context node
para[fn:last()]
selects the last para
child of the context node
*/para
selects all para
grandchildren of the context node
/book/chapter[5]/section[2]
selects the second section
of the fifth chapter
of the book
whose parent is the document node that contains the context node
chapter//para
selects the para
element descendants of the chapter
element children of the context node
//para
selects all the para
descendants of the root document node and thus selects all para
elements in the same document as the context node
//@version
selects all the version
attribute nodes that are in the same document as the context node
//list/member
selects all the member
elements in the same document as the context node that have a list
parent
.//para
selects the para
element descendants of the context node
..
selects the parent of the context node
../@lang
selects the lang
attribute of the parent of the context node
para[@type="warning"]
selects all para
children of the context node that have a type
attribute with value warning
para[@type="warning"][5]
selects the fifth para
child of the context node that has a type
attribute with value warning
para[5][@type="warning"]
selects the fifth para
child of the context node if that child has a type
attribute with value warning
chapter[title="Introduction"]
selects the chapter
children of the context node that have one or more title
children whose typed value is equal to the string Introduction
chapter[title]
selects the chapter
children of the context node that have one or more title
children
employee[@secretary and @assistant]
selects all the employee
children of the context node that have both a secretary
attribute and an assistant
attribute
book/(chapter|appendix)/section
selects every section
element that has a parent that is either a chapter
or an appendix
element, that in turn is a child of a book
element that is a child of the context node.
If E
is any expression that returns a sequence of nodes, then the expression E/.
returns the same nodes in document order, with duplicates eliminated based on node identity.
XQuery supports operators to construct, filter, and combine sequences of items. Sequences are never nested—for example, combining the values 1, (2, 3), and ( ) into a single sequence results in the sequence (1, 2, 3).
[28] | Expr |
::= | ExprSingle ("," ExprSingle)* |
[46] | RangeExpr |
::= | AdditiveExpr ( "to" AdditiveExpr )? |
[Definition: One way to construct a sequence is by using the comma operator, which evaluates each of its operands and concatenates the resulting sequences, in order, into a single result sequence.] Empty parentheses can be used to denote an empty sequence.
A sequence may contain duplicate atomic values or nodes, but a sequence is never an item in another sequence. When a new sequence is created by concatenating two or more input sequences, the new sequence contains all the items of the input sequences and its length is the sum of the lengths of the input sequences.
Note:
In places where the grammar calls for ExprSingle, such as the arguments of a function call, any expression that contains a top-level comma operator must be enclosed in parentheses.
Here are some examples of expressions that construct sequences:
The result of this expression is a sequence of five integers:
(10, 1, 2, 3, 4)
This expression combines four sequences of length one, two, zero, and two, respectively, into a single sequence of length five. The result of this expression is the sequence 10, 1, 2, 3, 4
.
(10, (1, 2), (), (3, 4))
The result of this expression is a sequence containing all salary
children of the context node followed by all bonus
children.
(salary, bonus)
Assuming that $price
is bound to the value 10.50
, the result of this expression is the sequence 10.50, 10.50
.
($price, $price)
A range expression can be used to construct a sequence of consecutive integers. Each of the operands of the to
operator is converted as though it was an argument of a function with the expected parameter type xs:integer?
. If either operand is an empty sequence, or if the integer derived from the first operand is greater than the integer derived from the second operand, the result of the range expression is an empty sequence. Otherwise, the result is a sequence containing
the two integer operands and every integer between the two operands, in increasing order.
This example uses a range expression as one operand in constructing a sequence. It evaluates to the sequence 10, 1, 2, 3, 4
.
(10, 1 to 4)
This example constructs a sequence of length one containing the single integer 10
.
10 to 10
The result of this example is a sequence of length zero.
15 to 10
This example uses the fn:reverse
function to construct a sequence of six integers in decreasing order. It evaluates to the sequence 15, 14, 13, 12, 11, 10
.
fn:reverse(10 to 15)
[74] | FilterExpr |
::= | PrimaryExpr PredicateList |
[75] | PredicateList |
::= | Predicate* |
A filter expression consists simply of a primary expression followed by zero or more predicates. The result of the filter expression consists of all the items returned by the primary expression for which all the predicates are true. If no predicates are specified, the result is simply the result of the primary expression. This result may contain nodes, atomic values, or any combination of these. The ordering of the items returned by a filter expression is the same as their order in the result of the primary expression. Context positions are assigned to items based on their ordinal position in the result sequence. The first context position is 1.
Here are some examples of filter expressions:
Given a sequence of products in a variable, return only those products whose price is greater than 100.
$products[price gt 100]
List all the integers from 1 to 100 that are divisible by 5. (See 3.3.1 Constructing Sequences for an explanation of the to
operator.)
(1 to 100)[. mod 5 eq 0]
The result of the following expression is the integer 25:
(21 to 29)[5]
The following example illustrates the use of a filter expression as a step in a path expression. It returns the last chapter or appendix within the book bound to variable $book
:
$book/(chapter | appendix)[fn:last()]
The following example also illustrates the use of a filter expression as a step in a path expression. It returns the element node within the specified document whose ID value is "tiger":
fn:doc("zoo.xml")/fn:id('tiger')
[49] | UnionExpr |
::= | IntersectExceptExpr ( ("union" | "|") IntersectExceptExpr )* |
[50] | IntersectExceptExpr |
::= | InstanceofExpr ( ("intersect" | "except") InstanceofExpr )* |
XQuery provides the following operators for combining sequences of nodes:
The union
and |
operators are equivalent. They take two node sequences as operands and return a sequence containing all the nodes that occur in either of the operands.
The intersect
operator takes two node sequences as operands and returns a sequence containing all the nodes that occur in both operands.
The except
operator takes two node sequences as operands and returns a sequence containing all the nodes that occur in the first operand but not in the second operand.
All these operators eliminate duplicate nodes from their result sequences based on node identity. If ordering mode is ordered
, the resulting sequence is returned in document order; otherwise it is returned in implementation-dependent order.
If an operand of union
, intersect
, or except
contains an item that is not a node, a type error is raised.[err:XP0004][err:XP0006]
Here are some examples of expressions that combine sequences. Assume the existence of three element nodes that we will refer to by symbolic names A, B, and C. Assume that the variables $seq1
, $seq2
and $seq3
are bound to the following sequences of these nodes:
$seq1
is bound to (A, B)
$seq2
is bound to (A, B)
$seq3
is bound to (B, C)
Then:
$seq1 union $seq2
evaluates to the sequence (A, B).
$seq2 union $seq3
evaluates to the sequence (A, B, C).
$seq1 intersect $seq2
evaluates to the sequence (A, B).
$seq2 intersect $seq3
evaluates to the sequence containing B only.
$seq1 except $seq2
evaluates to the empty sequence.
$seq2 except $seq3
evaluates to the sequence containing A only.
In addition to the sequence operators described here, [XQuery 1.0 and XPath 2.0 Functions and Operators] includes functions for indexed access to items or sub-sequences of a sequence, for indexed insertion or removal of items in a sequence, and for removing duplicate items from a sequence.
XQuery provides arithmetic operators for addition, subtraction, multiplication, division, and modulus, in their usual binary and unary forms.
[47] | AdditiveExpr |
::= | MultiplicativeExpr ( ("+" | "-") MultiplicativeExpr )* |
[48] | MultiplicativeExpr |
::= | UnionExpr ( ("*" | "div" | "idiv" | "mod") UnionExpr )* |
[55] | UnaryExpr |
::= | ("-" | "+")* ValueExpr |
[56] | ValueExpr |
::= | ValidateExpr | PathExpr |
A subtraction operator must be preceded by whitespace if it could otherwise be interpreted as part of the previous token. For example, a-b
will be interpreted as a name, but a - b
and a -b
will be interpreted as arithmetic operations.
The first step in evaluating an arithmetic expression is to evaluate its operands. The order in which the operands are evaluated is implementation-dependent.
Each operand is evaluated by applying the following steps, in order:
Atomization is applied to the operand. The result of this operation is called the atomized operand.
If the atomized operand is an empty sequence, the result of the arithmetic expression is an empty sequence, and the implementation need not evaluate the other operand or apply the operator. However, an implementation may choose to evaluate the other operand in order to determine whether it raises an error.
If the atomized operand is a sequence of length greater than one, a type error is raised.[err:XP0004][err:XP0006]
If the atomized operand is of type xdt:untypedAtomic
, it is cast to xs:double
. If the cast fails, a dynamic error is raised.[err:XP0021]
After evaluation of the operands, if the types of the operands are a valid combination for the given arithmetic operator, the operator is applied to the operands, resulting in an atomic value or a dynamic error (for example, an error might result from dividing by zero.) The combinations of atomic types that are accepted by the various arithmetic operators, and their respective result types, are listed in B.2 Operator Mapping together with the operator functions that define the semantics of the operator for each type combination, including the dynamic errors that can be raised by the operator. The definitions of the operator functions are found in [XQuery 1.0 and XPath 2.0 Functions and Operators].
If the types of the operands, after evaluation, are not a valid combination for the given operator, according to the rules in B.2 Operator Mapping, a type error is raised.[err:XP0004][err:XP0006]
XQuery supports two division operators named div
and idiv
. Each of these operators accepts two operands of any numeric type. As described in [XQuery 1.0 and XPath 2.0 Functions and Operators], $arg1 idiv $arg2
is equivalent to ($arg1 div $arg2) cast as xs:integer
except for error cases.
Here are some examples of arithmetic expressions:
The first expression below returns the xs:decimal
value -1.5
, and the second expression returns the xs:integer
value -1
:
-3 div 2 -3 idiv 2
Subtraction of two date values results in a value of type xdt:dayTimeDuration
:
$emp/hiredate - $emp/birthdate
This example illustrates the difference between a subtraction operator and a hyphen:
$unit-price - $unit-discount
Unary operators have higher precedence than binary operators, subject of course to the use of parentheses. Therefore, the following two examples have different meanings:
-$bellcost + $whistlecost -($bellcost + $whistlecost)
Note:
Multiple consecutive unary arithmetic operators are permitted by XQuery for compatibility with [XPath 1.0].
Comparison expressions allow two values to be compared. XQuery provides three kinds of comparison expressions, called value comparisons, general comparisons, and node comparisons.
[45] | ComparisonExpr |
::= | RangeExpr ( (ValueComp |
[58] | ValueComp |
::= | "eq" | "ne" | "lt" | "le" | "gt" | "ge" |
[57] | GeneralComp |
::= | "=" | "!=" | "<" | "<=" | ">" | ">=" |
[59] | NodeComp |
::= | "is" | "<<" | ">>" |
The value comparison operators are eq
, ne
, lt
, le
, gt
, and ge
. Value comparisons are used for comparing single values.
The first step in evaluating an value comparison is to evaluate its operands. The order in which the operands are evaluated is implementation-dependent. Each operand is evaluated by applying the following steps, in order:
Atomization is applied to the operand. The result of this operation is called the atomized operand.
If the atomized operand is an empty sequence, the result of the value comparison is an empty sequence, and the implementation need not evaluate the other operand or apply the operator. However, an implementation may choose to evaluate the other operand in order to determine whether it raises an error.
If the atomized operand is a sequence of length greater than one, a type error is raised.[err:XP0004][err:XP0006]
If the atomized operand is of type xdt:untypedAtomic
, it is cast to xs:string
.
Note:
The purpose of this rule is to make value comparisons transitive. Users should be aware that the general comparison operators have a different rule for casting of xdt:untypedAtomic
operands. Users should also be aware that transitivity of value comparisons may be compromised by loss of precision during type conversion (for example, two xs:integer
values that differ slightly may both be considered equal to the same xs:float
value because xs:float
has
less precision than xs:integer
).
After evaluation of the operands, if the types of the operands are a valid combination for the given operator, the operator is applied to the operands. The combinations of atomic types that are accepted by the various value comparison operators, and their respective result types, are listed in B.2 Operator Mapping together with the operator functions that define the semantics of the operator for each type combination. The definitions of the operator functions are found in [XQuery 1.0 and XPath 2.0 Functions and Operators].
Informally, if both atomized operands consist of exactly one atomic value, then the result of the comparison is true
if the value of the first operand is (equal, not equal, less than, less than or equal, greater than, greater than or equal) to the value of the second operand; otherwise the result of the comparison is false
.
If the types of the operands, after evaluation, are not a valid combination for the given operator, according to the rules in B.2 Operator Mapping, a type error is raised.[err:XP0004][err:XP0006]
Here are some examples of value comparisons:
The following comparison is true only if $book1
has exactly one author
subelement and its typed value is "Kennedy" as an instance of xs:string
or xdt:untypedAtomic
. If $book1
has more than one author
subelement, a type error is raised.[err:XP0004][err:XP0006] If $book1
has no author
subelement, the result of the expression is the empty sequence.
$book1/author eq "Kennedy"
The following path expression contains a predicate that selects products whose weight is greater than 100. For any product that does not have a weight
subelement, the value of the predicate is the empty sequence, and the product is not selected:
//product[weight gt 100]
The following comparisons are true because, in each case, the two constructed nodes have the same value after atomization, even though they have different identities and/or names:
<a>5</a> eq <a>5</a>
<a>5</a> eq <b>5</b>
The following comparison is true if my:hatsize
and my:shoesize
are both user-defined types that are derived by restriction from a primitive numeric type:
my:hatsize(5) eq my:shoesize(5)
The general comparison operators are =
, !=
, <
, <=
, >
, and >=
. General comparisons are existentially quantified comparisons that may be applied to operand sequences of any length. The result of a general comparison that does not raise an error is always true
or false
.
A general comparison is evaluated by applying the following rules, in order:
Atomization is applied to each operand. After atomization, each operand is a sequence of atomic values.
The result of the comparison is true
if and only if there is a pair of atomic values, one in the first operand sequence and the other in the second operand sequence, that have the required magnitude relationship. Otherwise the result of the comparison is false
. The magnitude relationship between two atomic values is determined by applying the following rules. If a cast
operation called for by these rules is not successful, a dynamic error is raised.
[err:XP0021]
Note:
The purpose of these rules is to preserve compatibility with XPath 1.0, in which (for example) x < 17
is a numeric comparison if x
is an untyped value. Users should be aware that the value comparison operators have different rules for casting of xdt:untypedAtomic
operands.
If one of the atomic values is an instance of xdt:untypedAtomic
and the other is an instance of a numeric type, then the xdt:untypedAtomic
value is cast to the type xs:double
.
If one of the atomic values is an instance of xdt:untypedAtomic
and the other is an instance of xdt:untypedAtomic
or xs:string
, then the xdt:untypedAtomic
value (or values) is (are) cast to the type xs:string
.
If one of the atomic values is an instance of xdt:untypedAtomic
and the other is not an instance of xs:string
, xdt:untypedAtomic
, or any numeric type, then the xdt:untypedAtomic
value is cast to the dynamic type of the other value.
After performing the conversions described above, the atomic values are compared using one of the value comparison operators eq
, ne
, lt
, le
, gt
, or ge
, depending on whether the general comparison operator was =
, !=
, <
, <=
, >
, or >=
. The values have the required magnitude relationship if and only if the result of this value
comparison is true
.
When evaluating a general comparison in which either operand is a sequence of items, an implementation may return true
as soon as it finds an item in the first operand and an item in the second operand that have the required magnitude relationship. Similarly, a general comparison may raise a dynamic error as soon as it encounters an error in evaluating either operand, or in comparing a pair of items from the two operands. As a
result of these rules, the result of a general comparison is not deterministic in the presence of errors.
Here are some examples of general comparisons:
The following comparison is true if the typed value of any author
subelement of $book1
is "Kennedy" as an instance of xs:string
or xdt:untypedAtomic
:
$book1/author = "Kennedy"
The following example contains three general comparisons. The value of the first two comparisons is true
, and the value of the third comparison is false
. This example illustrates the fact that general comparisons are not transitive.
(1, 2) = (2, 3) (2, 3) = (3, 4) (1, 2) = (3, 4)
The following example contains two general comparisons, both of which are true
. This example illustrates the fact that the =
and !=
operators are not inverses of each other.
(1, 2) = (2, 3) (1, 2) != (2, 3)
Suppose that $a
, $b
, and $c
are bound to element nodes with type annotation xdt:untypedAtomic
, with string values "1
", "2
", and "2.0
" respectively. Then ($a, $b) = ($c, 3.0)
returns false
, because $b
and $c
are compared as strings. However, ($a, $b) = ($c, 2.0)
returns true
, because
$b
and 2.0
are compared as numbers.
Node comparisons are used to compare two nodes, by their identity or by their document order. The result of a node comparison is defined by the following rules:
The operands of a node comparison are evaluated in implementation-dependent order.
Each operand must be either a single node or an empty sequence; otherwise a type error is raised.[err:XP0004][err:XP0006]
If either operand is an empty sequence, the result of the comparison is an empty sequence, and the implementation need not evaluate the other operand or apply the operator. However, an implementation may choose to evaluate the other operand in order to determine whether it raises an error.
A comparison with the is
operator is true
if the two operand nodes have the same identity, and are thus the same node; otherwise it is false
. See [XQuery 1.0 and XPath 2.0 Data Model] for a definition of node identity.
A comparison with the <<
operator returns true
if the left operand node precedes the right operand node in document order; otherwise it returns false
.
A comparison with the >>
operator returns true
if the left operand node follows the right operand node in document order; otherwise it returns false
.
Here are some examples of node comparisons:
The following comparison is true only if the left and right sides each evaluate to exactly the same single node:
/books/book[isbn="1558604820"] is /books/book[call="QA76.9 C3845"]
The following comparison is false because each constructed node has its own identity:
<a>5</a> is <a>5</a>
The following comparison is true only if the node identified by the left side occurs before the node identified by the right side in document order:
/transactions/purchase[parcel="28-451"] << /transactions/sale[parcel="33-870"]
A logical expression is either an and-expression or an or-expression. If a logical expression does not raise an error, its value is always one of the boolean values true
or false
.
[43] | OrExpr |
::= | AndExpr ( "or" AndExpr )* |
[44] | AndExpr |
::= | ComparisonExpr ( "and" ComparisonExpr )* |
The first step in evaluating a logical expression is to find the effective boolean value of each of its operands (see 2.4.3 Effective Boolean Value).
The value of an and-expression is determined by the effective boolean values (EBV's) of its operands, as shown in the following table:
AND: | EBV2 = true |
EBV2 = false |
error in EBV2 |
EBV1 = true |
true |
false |
error |
EBV1 = false |
false |
false |
either false or error |
error in EBV1 | error | either false or error |
error |
The value of an or-expression is determined by the effective boolean values (EBV's) of its operands, as shown in the following table:
OR: | EBV2 = true |
EBV2 = false |
error in EBV2 |
EBV1 = true |
true |
true |
either true or error |
EBV1 = false |
true |
false |
error |
error in EBV1 | either true or error |
error | error |
The order in which the operands of a logical expression are evaluated is implementation-dependent. The tables above are defined in such a way that an or-expression can return true
if the first expression evaluated is true, and it can raise an error if evaluation of the first expression raises an error. Similarly, an and-expression can return false
if the first expression evaluated is false, and it can raise an error if evaluation of the first expression raises an error. As a result of these rules, a logical expression is not deterministic in the presence of errors, as illustrated in the examples below.
Here are some examples of logical expressions:
The following expressions return true
:
1 eq 1 and 2 eq 2
1 eq 1 or 2 eq 3
The following expression may return either false
or raise a dynamic error:
1 eq 2 and 3 idiv 0 = 1
The following expression may return either true
or raise a dynamic error:
1 eq 1 or 3 idiv 0 = 1
The following expression must raise a dynamic error:
1 eq 1 and 3 idiv 0 = 1
In addition to and- and or-expressions, XQuery provides a function named fn:not
that takes a general sequence as parameter and returns a boolean value. The fn:not
function is defined in [XQuery 1.0 and XPath 2.0 Functions and Operators]. The fn:not
function reduces its parameter to an effective boolean value. It then returns true
if the effective boolean value of
its parameter is false
, and false
if the effective boolean value of its parameter is true
. If an error is encountered in finding the effective boolean value of its operand, fn:not
raises the same error.
XQuery provides constructors that can create XML structures within a query. Constructors are provided for element, attribute, document, text, comment, and processing instruction nodes. Two kinds of constructors are provided: direct constructors, which use an XML-like notation, and computed constructors, which use a notation based on enclosed expressions.
This section contains a conceptual description of the semantics of various kinds of constructor expressions. An XQuery implementation is free to use any implementation technique that produces the same result as the processing steps described in this section.
An element constructor creates an element node. [Definition: A direct element constructor is a form of element constructor in which the name of the constructed element is a constant.] Direct element constructors are based on standard XML notation. For example, the following expression is a direct element constructor that creates a book
element containing an attribute and some nested
elements:
<book isbn="isbn-0060229357"> <title>Harold and the Purple Crayon</title> <author> <first>Crockett</first> <last>Johnson</last> </author> </book>
If the element name in a direct element constructor has a namespace prefix, the namespace prefix is resolved to a namespace URI using the statically known namespaces. If the element name has no namespace prefix, it is implicitly qualified by the default element/type namespace. Note that both the statically known namespaces and the default element/type namespace may be affected by namespace declaration attributes found inside the element constructor. The namespace prefix of the element name is retained after expansion of the QName, as described in [XQuery 1.0 and XPath 2.0 Data Model]. The resulting expanded QName becomes the name of the constructed element node.
In a direct element constructor, the name used in the end tag must exactly match the name used in the corresponding start tag, including its prefix or absence of a prefix.
In a direct element constructor, curly braces { } delimit enclosed expressions, distinguishing them from literal text. Enclosed expressions are evaluated and replaced by their value, as illustrated by the following example:
<example> <p> Here is a query. </p> <eg> $b/title </eg> <p> Here is the result of the query. </p> <eg>{ $b/title }</eg> </example>
The above query might generate the following result (whitespace has been added for readability to this result and other result examples in this document):
<example> <p> Here is a query. </p> <eg> $b/title </eg> <p> Here is the result of the query. </p> <eg><title>Harold and the Purple Crayon</title></eg> </example>
Since XQuery uses curly braces to denote enclosed expressions, some convention is needed to denote a curly brace used as an ordinary character. For this purpose, a pair of identical curly brace characters within the content of an element or attribute are interpreted by XQuery as a single curly brace character (that is, the pair "{{
" represents the character "{
" and the pair "}}
" represents the character "}
".) Alternatively, the character references
{
and }
can be used to denote curly brace characters. A single left curly brace ("{
") is interpreted as the beginning delimiter for an enclosed expression. A single right curly brace ("}
") without a matching left curly brace is treated as a static error.[err:XP0003]
The result of an element constructor is a new element node, with its own node identity. All the attribute and descendant nodes of the new element node are also new nodes with their own identities, even if they are copies of existing nodes.
The Base URI of a constructed element node is taken from the static context. The Base URIs of the copied descendant nodes are also taken from the static context rather than by preserving their original Base URIs. If no Base URI is defined in the static context, the Base URIs of the constructed and copied nodes are set to the empty sequence.
The start tag of a direct element constructor may contain one or more attributes. As in XML, each attribute is specified by a name and a value. In a direct element constructor, the name of each attribute is specified by a constant QName, and the value of the attribute is specified by a string of characters enclosed in single or double quotes. As in the main content of the element constructor, an attribute value may contain expressions enclosed in curly braces, which are evaluated and replaced by their value during processing of the element constructor.
Each attribute in a direct element constructor creates a new attribute node, with its own node identity, whose parent is the constructed element node. However, note that namespace declaration attributes (see 3.7.1.2 Namespace Declaration Attributes) do not create attribute nodes.
If an attribute name has a namespace prefix, the prefix is resolved to a namespace URI using the statically known namespaces. If the attribute name has no namespace prefix, the attribute is in no namespace. Note that the statically known namespaces for used in resolving an attribute name may be affected by namespace declaration attributes that are found inside the same element constructor. The namespace prefix of the attribute name is retained after expansion of the QName, as described in [XQuery 1.0 and XPath 2.0 Data Model]. The resulting expanded QName becomes the name of the constructed attribute node.
If the attributes in a direct element constructor do not have distinct names, a static error is raised. [err:XQ0040]
Conceptually, an attribute (other than a namespace declaration attribute) in a direct element constructor is processed by the following steps:
Each consecutive sequence of literal characters in the attribute content is treated as a string containing those characters. Whitespace in attribute content is normalized according to the rules for "Attribute Value Normalization" in Section 3.3.3 of [XML 1.0] (if the XML and Names 1.1 Feature is supported, the rules in Section 3.3.3 of [XML 1.1] apply).
Predefined entity references and character references in the attribute content are expanded into their referenced strings, as described in 3.1.1 Literals.
Each enclosed expression is converted to a string as follows:
Atomization is applied to the value of the enclosed expression, converting it to a sequence of atomic values.
If the result of atomization is an empty sequence, the result is the zero-length string. Otherwise, each atomic value in the atomized sequence is cast into a string.
The individual strings resulting from the previous step are merged into a single string by concatenating them with a single space character between each pair.
Adjacent strings resulting from the above steps are concatenated with no intervening blanks. The resulting string becomes the string value of the attribute node. The attribute node is given an initial type annotation of xdt:untypedAtomic
(this type annotation may change during validation of the parent element).
Example:
<shoe size="7"/>
The string value of the size
attribute is "7
".
Example:
<shoe size="{7}"/>
The string value of the size
attribute is "7
".
Example:
<shoe size="{()}"/>
The string value of the size
attribute is the zero-length string.
Example:
<chapter ref="[{1, 5 to 7, 9}]"/>
The string value of the ref
attribute is "[1 5 6 7 9]
".
Example:
<shoe size="As big as {$hat/@size}"/>
The string value of the size
attribute is the string "As big as
", concatenated with the string value of the node denoted by the expression $hat/@size
.
The names of a constructed element and its attributes may be qualified names that include namespace prefixes. Namespace prefixes can be bound to namespaces in the Prolog or by namespace declaration attributes. It is a static error to use a namespace prefix that has not been bound to a namespace.[err:XP0008]
[Definition: A namespace declaration attribute is used inside a direct element constructor. Its purpose is to bind a namespace prefix or to set the default element/type namespace for the constructed element node, including its attributes.] Syntactically, a namespace declaration attribute has the form of an attribute with
namespace prefix xmlns
, or with name xmlns
and no namespace prefix. The value of a namespace declaration attribute must be a StringLiteral containing a valid URI, or a zero-length string; otherwise a static error is raised. [err:XQ0022][err:XQ0046] All the namespace declaration attributes of a given
element must have distinct names. [err:XQ0071] Each namespace declaration attribute is processed as follows:
If the name of the namespace declaration attribute has the prefix xmlns
, the local part of the name must not be xml
or xmlns
. [err:XQ0070] The local part of the name is interpreted as a namespace prefix and the value of the attribute is interpreted as a namespace URI. This prefix and URI are added to the statically known namespaces of the constructor
expression (overriding any existing binding of the given prefix), and are also added as a namespace binding to the in-scope namespaces of the constructed element. If the namespace URI is a zero-length string, any existing namespace binding for the given prefix is removed from the in-scope namespaces of the constructed element, and from the statically known namespaces of the constructor expression.
If the name of the namespace declaration attribute is xmlns
with no prefix, the value of the attribute is interpreted as a namespace URI. This URI specifies the default element/type namespace of the constructor expression (overriding any existing default), and is added (with no prefix) to the in-scope namespaces of the constructed element (overriding any
existing namespace binding with no prefix). If the namespace URI is a zero-length string, the default element/type namespace of the constructor expression is set to "none," and any no-prefix namespace binding is removed from the in-scope namespaces of the constructed element.
A namespace declaration attribute does not cause an attribute node to be created.
The following examples illustrate namespace declaration attributes:
In this element constructor, a namespace declaration attribute is used to set the default element/type namespace to http://example.org/animals
:
<cat xmlns = "http://example.org/animals"> <breed>Persian</breed> </cat>
In this element constructor, namespace declaration attributes are used to bind the namespace prefixes metric
and english
:
<box xmlns:metric = "http://example.org/metric/units" xmlns:english = "http://example.org/english/units"> <height> <metric:meters>3</metric:meters> </height> <width> <english:feet>6</english:feet> </width> <depth> <english:inches>18</english:inches> </depth> </box>
The part of a direct element constructor between the start tag and the end tag is called the content of the element constructor. This content may consist of text characters (parsed as ElementContentChar), nested direct constructors, CdataSections, character and predefined entity references, and expressions enclosed in curly braces. In general, the value of an enclosed expression may be any sequence of nodes and/or atomic values. Enclosed expressions can be used in the content of an element constructor to compute both the content and the attributes of the constructed node.
Conceptually, the content of an element constructor is processed as follows:
The content is evaluated to produce a sequence of nodes called the content sequence, as follows:
Within sequences of characters parsed as ElementContentChar, line endings are normalized according to the rules for "End-of-Line Handling" in Section 2.11 of [XML 1.0] (if the XML and Names 1.1 Feature is supported, the rules in Section 2.11 of [XML 1.1] apply).
Predefined entity references and character references are expanded into their referenced strings, as described in 3.1.1 Literals. Characters inside a CDataSection, including special characters such as <
and &
, are treated as literal characters rather than as delimiters (except for the sequence ]]>
, which terminates the CDataSection).
Each consecutive sequence of literal characters evaluates to a single text node containing the characters. However, if the sequence consists entirely of boundary whitespace and the XMLSpace policy in the static context is strip
, then no text node is generated.
Each nested direct constructor is evaluated according to the rules in 3.7.1 Direct Element Constructors or 3.7.2 Other Direct Constructors, resulting in a new element, comment, or processing instruction node.
Enclosed expressions are evaluated as follows:
For each adjacent sequence of one or more atomic values returned by an enclosed expression, a new text node is constructed, containing the result of casting each atomic value to a string, with a single space character inserted between adjacent values.
Note:
The insertion of blank characters between adjacent values applies even if one or both of the values is a zero-length string.
For each node returned by an enclosed expression, a new copy is made of the given node and all nodes that have the given node as an ancestor, collectively referred to as copied nodes. The properties of the copied nodes are as follows:
Each copied node receives a new node identity.
The parent
, children
, and attributes
properties of the copied nodes are set so as to preserve their inter-node relationships. For the topmost node (the node directly returned by the enclosed expression), the parent
property is empty.
The base-uri
properties of the copied nodes are taken from Base URI in the static context. If no Base URI is defined in the static context, the base-uri
properties are empty.
If construction mode in the static context is strip
:
The type-name
property of each copied element node is set to xdt:untyped
and its nilled
property is set to false
.
The type-name
property of each copied attribute node is set to xdt:untypedAtomic
.
The string-value
of each copied element and attribute node remains unchanged, and its typed-value
becomes equal to its string-value
as an instance of xdt:untypedAtomic
.
Note:
Implementations that store only the typed value of a node are required at this point to convert the typed value to a string form.)
On the other hand, if construction mode in the static context is preserve
, the type-name
, nilled
, string-value
, and typed-value
properties of the copied nodes are preserved.
The in-scope-namespaces
property of a copied element node is determined by the following rules. In applying these rules, the default namespace or absence of a default namespace is treated like any other namespace binding:
If namespace inheritance mode in the static context is no
, the in-scope-namespaces
of the original copy are preserved. The new copy has exactly the same in-scope-namespaces
as the original node.
If namespace inheritance mode in the static context is yes
, the new copy inherits the in-scope-namespaces
of its new parent (the constructed node), augmented and overridden where necessary by the in-scope-namespaces
of the original copy.
All other properties of the copied nodes are preserved.
Adjacent text nodes in the content sequence are merged into a single text node by concatenating their contents, with no intervening blanks. After concatenation, any text node whose content is a zero-length string is deleted from the content sequence.
If the content sequence contains a document node, the document node is replaced in the content sequence by its children.
If the content sequence contains an attribute node following a node that is not an attribute node, a type error is raised.[err:XQ0024]
The properties of the newly constructed element node are determined as follows:
node-name
is the expanded QName resulting from resolving the element name in the start tag, including its original namespace prefix (if any), as described in 3.7.1 Direct Element Constructors.
base-uri
is taken from Base URI in the static context. If no Base URI is defined in the static context, the base-uri
property is empty.
parent
is empty.
attributes
consist of all the attributes specified in the start tag as described in 3.7.1.1 Attributes, together with all the attribute nodes in the content sequence, in implementation-dependent order. If two or more of these attributes have the same name, a dynamic error is raised.[err:XQ0025]
children
consist of all the element, text, comment, and processing instruction nodes in the content sequence.
in-scope-namespaces
consist of all the namespace bindings resulting from namespace declaration attributes as described in 3.7.1.2 Namespace Declaration Attributes, and possibly additional namespace bindings as described in 3.7.4 In-scope Namespaces of a Constructed Element.
The nilled
property is false
.
The string-value
property is equal to the concatenated contents of the text-node descendants in document order.
The typed-value
property is equal to the string-value
property, as an instance of xdt:untypedAtomic
.
If construction mode in the static context is strip
, the type-name
property is xdt:untyped
. On the other hand, if construction mode is preserve
, the type-name
property is xs:anyType
.
Example:
<a>{1}</a>
The constructed element node has one child, a text node containing the value "1
".
Example:
<a>{1, 2, 3}</a>
The constructed element node has one child, a text node containing the value "1 2 3
".
Example:
<c>{1}{2}{3}</c>
The constructed element node has one child, a text node containing the value "123
".
Example:
<b>{1, "2", "3"}</b>
The constructed element node has one child, a text node containing the value "1 2 3
".
Example:
<fact>I saw 8 cats.</fact>
The constructed element node has one child, a text node containing the value "I saw 8 cats.
".
Example:
<fact>I saw {5 + 3} cats.</fact>
The constructed element node has one child, a text node containing the value "I saw 8 cats.
".
Example:
<fact>I saw <howmany>{5 + 3}</howmany> cats.</fact>
The constructed element node has three children: a text node containing "I saw
", a child element node named howmany
, and a text node containing " cats.
". The child element node in turn has a single text node child containing the value "8
".
In a direct element constructor, whitespace characters may appear in element content. In some cases, enclosed expressions and/or nested elements may be separated only by whitespace characters. For example, in the expression below, the end-tag </title>
and the start-tag <author>
are separated by a newline character and four space characters:
<book isbn="isbn-0060229357"> <title>Harold and the Purple Crayon</title> <author> <first>Crockett</first> <last>Johnson</last> </author> </book>
[Definition: Whitespace characters that occur by themselves in the boundaries between tags and/or enclosed expressions are called boundary whitespace.] The XMLSpace policy in the static context controls whether boundary whitespace is preserved by element constructors. If XMLSpace policy is
strip
, boundary whitespace is not considered significant and is discarded. On the other hand, if XMLSpace policy is preserve
, boundary whitespace is considered significant and is preserved.
Example:
<cat> <breed>{$b}</breed> <color>{$c}</color> </cat>
The constructed cat
element node has two child element nodes named breed
and color
. Whitespace surrounding the child elements will be stripped away by the element constructor if XMLSpace policy is strip
.
Example:
<a> {"abc"} </a>
If XMLSpace policy is strip
, this example is equivalent to <a>abc</a>
. However, if XMLSpace policy is preserve
, this example is equivalent to <a> abc </a>
.
Example:
<a> z {"abc"}</a>
Since the whitespace surrounding the z
is not boundary whitespace, it is always preserved. This example is equivalent to <a> z abc</a>
.
For the purpose of the above rule, whitespace characters generated by character references such as  
or by CdataSections are not considered to be boundary whitespace, and are always preserved. Similarly, whitespace characters that are adjacent to a character reference or a CDataSection are always preserved.
Example:
<a> {"abc"}</a>
This example is equivalent to <a> abc</a>
, regardless of the XMLSpace policy.
It is important to remember that whitespace generated by an enclosed expression is never considered to be boundary whitespace, and is always preserved.
Example:
<a>{" "}</a>
This example is equivalent to <a> </a>
, regardless of the XMLSpace policy.
XQuery allows a query to generate a processing instruction or XML comment directly into the query result. This can be accomplished by using a direct processing instruction constructor or a direct comment constructor. In each case, the syntax of the constructor expression is based on the syntax of the equivalent construct in XML.
[97] | DirPIConstructor |
::= | "<?" PITarget (S DirPIContents)? "?>" |
[98] | DirPIContents |
::= | (Char* - (Char* '?>' Char*)) |
[95] | DirCommentConstructor |
::= | "<!--" DirCommentContents "-->" |
[96] | DirCommentContents |
::= | ((Char - '-') | ('-' (Char - '-')))* |
The target (PITarget
) of a processing instruction may not consist of the characters "XML" in any combination of upper and lower case. The content (DirPIContents
) of a processing instruction may not contain the string "?>
". The content (DirCommentContents
) of a comment may not contain two consecutive hyphens or end with a hyphen. These rules are syntactically enforced by the grammar shown above.
The following example illustrates a direct processing instruction constructor:
<?format role="output" ?>
The following example illustrates a direct comment constructor:
<!-- Tags are ignored in the following section -->
Note that an direct comment constructor actually constructs a comment node. An XQuery comment, on the other hand, (see 2.7 Comments) is simply a comment used in documenting a query, and is not evaluated. Consider the following example:
(: This is an XQuery comment :) <!-- This is an XML comment -->
The result of evaluating the above example is as follows:
<!-- This is an XML comment -->
[101] | ComputedConstructor |
::= | CompDocConstructor |
An alternative way to create nodes is by using a computed constructor. A computed constructor begins with a keyword that identifies the type of node to be created: element
, attribute
, document
, text
, processing-instruction
, or comment
.
For those kinds of nodes that have names (element, attribute, and processing instruction nodes), the keyword that specifies the node kind is followed by the name of the node to be created. This name may be specified either as a QName or as an expression enclosed in braces, called the name expression, that returns a value of type xs:QName
, xs:string
, or xdt:untypedAtomic
.
The final part of a computed constructor is an expression enclosed in braces, called the content expression, that generates the content of the node.
The following example illustrates the use of computed element and attribute constructors in a simple case where the names of the constructed nodes are constants. This example generates exactly the same result as the first example in 3.7.1 Direct Element Constructors:
element book { attribute isbn {"isbn-0060229357" }, element title { "Harold and the Purple Crayon"}, element author { element first { "Crockett" }, element last {"Johnson" } } }
[103] | CompElemConstructor |
::= | (("element" QName "{") | ("element" "{" Expr "}" "{")) ContentExpr? "}" |
[104] | ContentExpr |
::= | Expr |
[Definition: A computed element constructor creates an element node, allowing both the name and the content of the node to be computed.]
The name expression of a computed element constructor is processed as follows:
Atomization is applied to the value of the name expression. If the result of atomization is not a single atomic value of type xs:QName
, xs:string
, or xdt:untypedAtomic
, a type error is raised.[err:XP0004][err:XP0006]
If the atomized value of the name expression is of type xs:QName
, that expanded QName is used as the name of the constructed element, retaining the prefix part of the QName.
If the atomized value of the name expression is of type xs:string
or xdt:untypedAtomic
, that value is converted to an expanded QName. If the string value contains a namespace prefix, that prefix is resolved to a namespace URI using the statically known namespaces. If the string value contains no namespace prefix, it is treated as a local name in the
default element/type namespace. If conversion of the atomized name expression to an expanded QName is not successful, a dynamic error is raised. [err:XQ0074]
The content expression of a computed element constructor is processed in exactly the same way as an enclosed expression in the content of a direct element constructor, as described in Step 1d of 3.7.1.3 Content. The result of processing the content expression is a sequence of nodes called the content sequence. Processing of the computed element constructor then proceeds as follows:
Adjacent text nodes in the content sequence are merged into a single text node by concatenating their contents, with no intervening blanks. After concatenation, any text node whose content is a zero-length string is deleted from the content sequence.
If the content sequence contains a document node, the document node is replaced in the content sequence by its children.
If the content sequence contains an attribute node following a node that is not an attribute node, a type error is raised.[err:XQ0024]
The properties of the newly constructed element node are determined as follows:
node-name
is the expanded QName resulting from processing the name expression, as described above, including its namespace prefix.
base-uri
is taken from Base URI in the static context. If no Base URI is defined in the static context, the base-uri
property is empty.
parent
is empty.
attributes
consist of all the attribute nodes in the content sequence, in implementation-dependent order. If two or more of these attributes have the same name, a dynamic error is raised.[err:XQ0025]
children
consist of all the element, text, comment, and processing instruction nodes in the content sequence.
in-scope-namespaces
are computed as described in 3.7.4 In-scope Namespaces of a Constructed Element.
The nilled
property is false
.
The string-value
property is equal to the concatenated contents of the text-node descendants in document order.
The typed-value
property is equal to the string-value
property, as an instance of xdt:untypedAtomic
.
If construction mode in the static context is strip
, the type-name
property is xdt:untyped
. On the other hand, if construction mode is preserve
, the type-name
property is xs:anyType
.
A computed element constructor might be used to make a modified copy of an existing element. For example, if the variable $e
is bound to an element with numeric content, the following constructor might be used to create a new element with the same name and attributes as $e
and with numeric content equal to twice the value of $e
:
element {fn:node-name($e)} {$e/@*, 2 * fn:data($e)}
In this example, if $e
is bound by the expression let $e := <length units="inches">{5}</length>
, then the result of the example expression is the element <length units="inches">10</length>
.
Note:
The static type of the expression fn:node-name($e)
is xs:QName?
, denoting zero or one QName. Therefore, if the Static Typing Feature is in effect, the above example raises a static type error, since the name expression in a computed element constructor is required to return exactly one string or QName. In order to avoid the static type error, the name expression fn:node-name($e)
could be
rewritten as fn:exactly-one(fn:node-name($e))
. If the Static Typing Feature is not in effect, the example can be successfully evaluated as written, provided that $e
is bound to exactly one element node with numeric content.
One important purpose of computed constructors is to allow the name of a node to be computed. We will illustrate this feature by an expression that translates the name of an element from one language to another. Suppose that the variable $dict
is bound to a dictionary
element containing a sequence of entry
elements, each of which encodes translations for a specific word. Here is an example entry that encodes the German and Italian variants of the word
"address":
<entry word="address"> <variant xml:lang="de">Adresse</variant> <variant xml:lang="it">indirizzo</variant> </entry>
Suppose further that the variable $e
is bound to the following element:
<address>123 Roosevelt Ave. Flushing, NY 11368</address>
Then the following expression generates a new element in which the name of $e
has been translated into Italian and the content of $e
(including its attributes, if any) has been preserved. The first enclosed expression after the element
keyword generates the name of the element, and the second enclosed expression generates the content and attributes:
element {$dict/entry[@word=name($e)]/variant[@xml:lang="it"]} {$e/@*, $e/node()}
The result of this expression is as follows:
<indirizzo>123 Roosevelt Ave. Flushing, NY 11368</indirizzo>
Note:
As in the previous example, if the Static Typing Feature is in effect, the enclosed expression that computes the element name in the above computed element constructor must be wrapped in a call to the fn:exactly-one
function in order to avoid a static type error.
Additional examples of computed element constructors can be found in G.4 Recursive Transformations.
[105] | CompAttrConstructor |
::= | (("attribute" QName "{") | ("attribute" "{" Expr "}" "{")) Expr? "}" |
A computed attribute constructor creates a new attribute node, with its own node identity.
The name expression of a computed attribute constructor is processed as follows:
Atomization is applied to the result of the name expression. If the result of atomization is not a single atomic value of type xs:QName
, xs:string
, or xdt:untypedAtomic
, a type error is raised.[err:XP0004][err:XP0006]
If the atomized value of the name expression is of type xs:QName
, that expanded QName (including its prefix) is used as the name of the constructed attribute.
If the atomized value of the name expression is of type xs:string
or xdt:untypedAtomic
, that value is converted to an expanded QName. If the string value contains a namespace prefix, that prefix is resolved to a namespace URI using the statically known namespaces. If the string value contains no namespace prefix, it is treated as a local name in no
namespace. The resulting expanded QName is used as the name of the constructed attribute.
A dynamic error [err:XQ0044] is raised if the URI part of the resulting expanded QName is http://www.w3.org/2000/xmlns/
(corresponding to namespace prefix xmlns
) or if the resulting expanded QName is in no namespace and has local name xmlns
.
The content expression of a computed attribute constructor is processed as follows:
Atomization is applied to the result of the content expression, converting it to a sequence of atomic values.
If the result of atomization is an empty sequence, the value of the attribute is the zero-length string. Otherwise, each atomic value in the atomized sequence is cast into a string.
The individual strings resulting from the previous step are merged into a single string by concatenating them with a single space character between each pair. The resulting string is the string value of the new attribute node. The type-name
property of the new attribute node is xdt:untypedAtomic
. Its parent
property is empty.
Example:
attribute size {4 + 3}
The value of the size
attribute is "7
" and its type is xdt:untypedAtomic
.
Example:
attribute { if ($sex = "M") then "husband" else "wife" } { <a>Hello</a>, 1 to 3, <b>Goodbye</b> }
The name of the constructed attribute is either husband
or wife
. Its string value is "Hello 1 2 3 Goodbye
".
[102] | CompDocConstructor |
::= | "document" "{" Expr "}" |
All document node constructors are computed constructors. The result of a document node constructor is a new document node, with its own node identity.
A document node constructor is useful when the result of a query is to be a document in its own right. The following example illustrates a query that returns an XML document containing a root element named author-list
:
document { <author-list> {fn:doc("bib.xml")/bib/book/author} </author-list> }
The content expression of a document node constructor is processed in exactly the same way as an enclosed expression in the content of a direct element constructor, as described in Step 1d of 3.7.1.3 Content. The result of processing the content expression is a sequence of nodes called the content sequence. Processing of the document node constructor then proceeds as follows:
Adjacent text nodes in the content sequence are merged into a single text node by concatenating their contents, with no intervening blanks. After concatenation, any text node whose content is a zero-length string is deleted from the content sequence.
If the content sequence contains a document node, the document node is replaced in the content sequence by its children.
If the content sequence contains an attribute node, a type error is raised.[err:XP0004][err:XP0006]
The properties of the newly constructed document node are determined as follows:
base-uri
is taken from Base URI in the static context. If no Base URI is defined in the static context, the base-uri
property is empty.
children
consist of all the element, text, comment, and processing instruction nodes in the content sequence.
The unparsed-entities
and document-uri
properties are empty.
The string-value
and typed-value
properties are derived from the children
property as described in [XQuery 1.0 and XPath 2.0 Data Model].
No validation is performed on the constructed document node. The [XML 1.0] rules that govern the structure of an XML document (for example, the document node must have exactly one child that is an element node) are not enforced by the XQuery document node constructor.
[106] | CompTextConstructor |
::= | "text" "{" Expr "}" |
All text node constructors are computed constructors. The result of a text node constructor is a new text node, with its own node identity.
The content expression of a text node constructor is processed as follows:
Atomization is applied to the value of the content expression, converting it to a sequence of atomic values.
If the result of atomization is an empty sequence, no text node is constructed. Otherwise, each atomic value in the atomized sequence is cast into a string. If any of these atomic values cannot be cast into a string, a dynamic error [err:XQ0052] is raised.
The individual strings resulting from the previous step are merged into a single string by concatenating them with a single space character between each pair. The resulting string becomes the content of the constructed text node.
Note:
It is possible for a text node constructor to construct a text node containing a zero-length string. However, if used in the content of a constructed element or document node, such a text node will be deleted or merged with another text node.
The following example illustrates a text node constructor:
text {"Hello"}
[108] | CompPIConstructor |
::= | (("processing-instruction" NCName "{") | ("processing-instruction" "{" Expr "}" "{")) Expr? "}" |
A computed processing instruction constructor (CompPIConstructor) constructs a new processing instruction node with its own node identity. The name expression of a computed processing instruction constructor is processed as follows:
Atomization is applied to the value of the name expression. If the result of atomization is not a single atomic value of type xs:NCName
, xs:string
, or xdt:untypedAtomic
, a type error is raised.[err:XP0004][err:XP0006]
If the atomized value of the name expression is of type xs:string
or xdt:untypedAtomic
, that value is cast to the type xs:NCName
. If the value cannot be cast to xs:NCName
, a dynamic error is raised.[err:XQ0041]
The resulting NCName is then used as the name (target) of the newly constructed processing instruction node. However, a dynamic error is raised if the NCName is equal to "XML
" (in any combination of upper and lower case) [err:XQ0064].
The content expression of a computed processing instruction constructor is processed as follows:
Atomization is applied to the value of the content expression, converting it to a sequence of atomic values.
If the result of atomization is an empty sequence, it is replaced by a zero-length string. Otherwise, each atomic value in the atomized sequence is cast into a string. If any of these atomic values cannot be cast into a string, a dynamic error [err:XQ0052] is raised. If any of the resulting strings contains the string "?>
", a dynamic
error [err:XQ0026] is raised.
The individual strings resulting from the previous step are merged into a single string by concatenating them with a single space character between each pair. Leading whitespace is removed from the resulting string. The resulting string then becomes the content of the constructed processing instruction node.
The following example illustrates a computed processing instruction constructor:
let $target := "audio-output", $content := "beep" return processing-instruction {$target} {$content}
The processing instruction node constructed by this example might be serialized as follows:
<?audio-output beep?>
[107] | CompCommentConstructor |
::= | "comment" "{" Expr "}" |
A computed comment constructor (CompCommentConstructor) constructs a new comment node with its own node identity. The content expression of a computed comment constructor is processed as follows:
Atomization is applied to the value of the content expression, converting it to a sequence of atomic values.
If the result of atomization is an empty sequence, it is replaced by a zero-length string. Otherwise, each atomic value in the atomized sequence is cast into a string. If any of these atomic values cannot be cast into a string, a dynamic error [err:XQ0052] is raised.
The individual strings resulting from the previous step are merged into a single string by concatenating them with a single space character between each pair.
It is a dynamic error [err:XQ0072] if the result of the content expression of a computed comment constructor contains two adjacent hyphens or ends with a hyphen.
The following example illustrates a computed comment constructor:
let $homebase := "Houston" return comment {fn:concat($homebase, ", we have a problem.")}
The comment node constructed by this example might be serialized as follows:
<!--Houston, we have a problem.-->
An element node constructed by a direct or computed element constructor has an in-scope namespaces property that consists of a set of namespace bindings. The in-scope namespaces of an element node may affect the way the node is serialized (see 2.2.4 Serialization), and may also affect the behavior of certain functions that operate on
nodes, such as fn:name
. Note the difference between in-scope namespaces, which is a dynamic property of an element node, and statically known namespaces, which is a static property of an expression. Also note that one of the namespace bindings in the in-scope namespaces may have no prefix (denoting the default namespace for the given element). The in-scope
namespaces of a constructed element node consist of the following namespace bindings:
A namespace binding is created for each namespace declared in the current element constructor by a namespace declaration attribute.
A namespace binding is created for each namespace that is declared in a namespace declaration attribute of an ancestor element constructor and not overridden by the current element constructor or a lower-level ancestor.
A namespace binding is always created to bind the prefix xml
to the namespace URI http://www.w3.org/XML/1998/namespace
.
For each namespace used in the name of the constructed element or in the names of its attributes, a namespace binding must exist. If a namespace binding does not already exist for one of these namespaces, a new namespace binding is created for it. If the name of the node includes a prefix, that prefix is used in the namespace binding; if the name has no prefix, then a binding is created for the empty prefix. If this would result in a conflict, because it would require two different bindings of the same prefix, then the prefix used in the node name is changed to an arbitrary implementation-dependent prefix that does not cause such a conflict, and a namespace binding is created for this new prefix.
The following query serves as an example:
declare namespace p="http://example.com/ns/p"; declare namespace q="http://example.com/ns/q"; declare namespace f="http://example.com/ns/f"; <p:a q:b="{f:func(2)}" xmlns:r="http://example.com/ns/r"/>
The in-scope namespaces of the resulting p:a
element consists of the following namespace bindings:
p = "http://example.com/ns/p"
q = "http://example.com/ns/q"
r = "http://example.com/ns/r"
xml = "http://www.w3.org/XML/1998/namespace"
The namespace bindings for p
and q
are added to the result element because their respective namespaces are used in the names of the element and its attributes. The namespace binding r="http://example.com/ns/r"
is added to the in-scope namespaces of the constructed element because it is defined by a namespace declaration attribute, even though it is not used in a name.
No namespace binding corresponding to f="http://example.com/ns/f"
is created, because the namespace prefix f
appears only in the query prolog and is not used in an element or attribute name of the constructed node. This namespace binding does not appear in the query result, even though it is present in the statically known namespaces and is available for use during processing of the query.
Note that the following constructed element cannot be validated:
<p xsi:type="xs:integer">3</p>
The constructed element will have namespace bindings for the prefixes xsi
(because it is used in a name) and xml
(because it is defined for every constructed element node). During validation of the constructed element, the validator will be unable to interpret the namespace prefix xs
because it is has no namespace binding. Validation of this constructed element could be made possible by providing a namespace declaration attribute, as in the following example:
<p xmlns:xs="http://www.w3.org/2001/XMLSchema" xsi:type="xs:integer">3</p>
XQuery provides a feature called a FLWOR expression that supports iteration and binding of variables to intermediate results. This kind of expression is often useful for computing joins between two or more documents and for restructuring data. The name FLWOR, pronounced "flower", is suggested by the keywords for
, let
, where
, order by
, and return
.
[30] | FLWORExpr |
::= | (ForClause | LetClause)+ WhereClause? OrderByClause? "return" ExprSingle |
[31] | ForClause |
::= | "for" "$" VarName TypeDeclaration? PositionalVar? "in" ExprSingle ("," "$" VarName TypeDeclaration? PositionalVar? "in" ExprSingle)* |
[33] | LetClause |
::= | "let" "$" VarName TypeDeclaration? ":=" ExprSingle ("," "$" VarName TypeDeclaration? ":=" ExprSingle)* |
[110] | TypeDeclaration |
::= | "as" SequenceType |
[32] | PositionalVar |
::= | "at" "$" VarName |
[34] | WhereClause |
::= | "where" ExprSingle |
[35] | OrderByClause |
::= | ("order" "by" | "stable" "order" "by") OrderSpecList |
[36] | OrderSpecList |
::= | OrderSpec ("," OrderSpec)* |
[37] | OrderSpec |
::= | ExprSingle OrderModifier |
[38] | OrderModifier |
::= | ("ascending" | "descending")? (("empty" "greatest") | ("empty" "least"))? ("collation" StringLiteral)? |
The for
and let
clauses in a FLWOR expression generate an ordered sequence of tuples of bound variables, called the tuple stream. The optional where
clause serves to filter the tuple stream, retaining some tuples and discarding others. The optional order by
clause can be used to reorder the tuple stream. The return
clause constructs the result of the FLWOR expression. The return
clause is evaluated once for every tuple
in the tuple stream, after filtering by the where
clause, using the variable bindings in the respective tuples. The result of the FLWOR expression is an ordered sequence containing the results of these evaluations, concatenated as if by the comma operator.
The following example of a FLWOR expression includes all of the possible clauses. The for
clause iterates over all the departments in an input document, binding the variable $d
to each department number in turn. For each binding of $d
, the let
clause binds variable $e
to all the employees in the given department, selected from another input document. The result of the for
and let
clauses is a tuple stream in which
each tuple contains a pair of bindings for $d
and $e
($d
is bound to a department number and $e
is bound to a set of employees in that department). The where
clause filters the tuple stream by keeping only those binding-pairs that represent departments having at least ten employees. The order by
clause orders the surviving tuples in descending order by the average salary of the employees in the department. The return
clause constructs a new big-dept
element for each surviving tuple, containing the department number, headcount, and average salary.
for $d in fn:doc("depts.xml")/depts/deptno
let $e := fn:doc("emps.xml")/emps/emp[deptno = $d]
where fn:count($e) >= 10
order by fn:avg($e/salary) descending
return
<big-dept>
{
$d,
<headcount>{fn:count($e)}</headcount>,
<avgsal>{fn:avg($e/salary)}</avgsal>
}
</big-dept>
The clauses in a FLWOR expression are described in more detail below.
The purpose of the for
and let
clauses in a FLWOR expression is to produce a tuple stream in which each tuple consists of one or more bound variables.
The simplest example of a for
clause contains one variable and an associated expression. [Definition: The value of the expression associated with a variable in a for
clause is called the binding sequence for that variable.] The for
clause iterates over the items in the binding sequence, binding the variable to each item in turn. If ordering mode is ordered
, the resulting sequence of variable bindings is ordered according to the order of values in the binding sequence; otherwise the ordering of the variable bindings is implementation-dependent.
A for
clause may also contain multiple variables, each with an associated expression whose value is the binding sequence for that variable. In this case, the for
clause iterates each variable over its binding sequence. The resulting tuple stream contains one tuple for each combination of values in the respective binding sequences. If ordering mode is ordered
, the order of the tuple stream is determined primarily
by the order of the binding sequence of the leftmost variable, and secondarily by the binding sequences of the other variables, working from left to right. Otherwise, the ordering of the variable bindings is implementation-dependent.
A let
clause may also contain one or more variables, each with an associated expression. Unlike a for
clause, however, a let
clause binds each variable to the result of its associated expression, without iteration. The variable bindings generated by let
clauses are added to the binding tuples generated by the for
clauses. If there are no for
clauses, the let
clauses generate one tuple containing all the variable
bindings.
Although for
and let
clauses both bind variables, the manner in which variables are bound is quite different, as illustrated by the following examples. The first example uses a let
clause:
let $s := (<one/>, <two/>, <three/>)
return <out>{$s}</out>
The variable $s
is bound to the result of the expression (<one/>, <two/>, <three/>)
. Since there are no for
clauses, the let
clause generates one tuple that contains the binding of $s
. The return
clause is invoked for this tuple, creating the following output:
<out> <one/> <two/> <three/> </out>
The next example is a similar query that contains a for
clause instead of a let
clause:
for $s in (<one/>, <two/>, <three/>)
return <out>{$s}</out>
In this example, the variable $s
iterates over the given expression. If ordering mode is ordered
, $s
is first bound to <one/>
, then to <two/>
, and finally to <three/>
. One tuple is generated for each of these bindings, and the return
clause is invoked for each tuple, creating the following output:
<out> <one/> </out> <out> <two/> </out> <out> <three/> </out>
The following example illustrates how binding tuples are generated by a for
clause that contains multiple variables when ordering mode is ordered
.
for $i in (1, 2), $j in (3, 4)
The tuple stream generated by the above for
clause is as follows:
($i = 1, $j = 3) ($i = 1, $j = 4) ($i = 2, $j = 3) ($i = 2, $j = 4)
If ordering mode were unordered
, the for
clause in the above example would generate the same tuple stream but the order of the tuples would be implementation-dependent.
The scope of a variable bound in a for
or let
clause comprises all subexpressions of the containing FLWOR expression that appear after the variable binding. The scope does not include the expression to which the variable is bound. The following example illustrates how bindings in for
and let
clauses may reference variables that were bound in earlier clauses, or in earlier bindings in the same clause of the FLWOR expression:
for $x in $w, $a in f($x) let $y := g($a) for $z in p($x, $y) return q($x, $y, $z)
The for
and let
clauses of a given FLWOR expression may bind the same variable name more than once. In this case, each new binding occludes the previous one, which becomes inaccessible in the remainder of the FLWOR expression.
Each variable bound in a for
or let
clause may have an optional type declaration, which is a type declared using the syntax in 2.5.3 SequenceType Syntax. If the type of a value bound to the variable does not match the declared type according to the rules for SequenceType matching, a type error is
raised.[err:XP0004][err:XP0006] For example, the following expression raises a type error because the variable $salary
has a type declaration that is not satisfied by the value that is bound to the variable:
let $salary as xs:decimal := "cat" return $salary * 2
Each variable bound in a for
clause may have an associated positional variable that is bound at the same time. The name of the positional variable is preceded by the keyword at
. The positional variable always has an implied type of xs:integer
. As a variable iterates over the items in its binding sequence, its positional variable iterates over the integers that represent the ordinal positions of
those items in the binding sequence, starting with 1.
Positional variables are illustrated by the following for
clause:
for $car at $i in ("Ford", "Chevy"), $pet at $j in ("Cat", "Dog")
If ordering mode is ordered
, the tuple stream generated by the above for
clause is as follows:
($i = 1, $car = "Ford", $j = 1, $pet = "Cat") ($i = 1, $car = "Ford", $j = 2, $pet = "Dog") ($i = 2, $car = "Chevy", $j = 1, $pet = "Cat") ($i = 2, $car = "Chevy", $j = 2, $pet = "Dog")
If ordering mode is unordered
, the resulting tuple stream contains the same tuples, in implementation-dependent order.
The optional where
clause serves as a filter for the tuples of variable bindings generated by the for
and let
clauses. The expression in the where
clause, called the where-expression, is evaluated once for each of these tuples. If the effective boolean value of the where-expression is true
, the tuple is retained and its variable bindings are used in an execution of the
return
clause. If the effective boolean value of the where-expression is false
, the tuple is discarded. The effective boolean value of an expression is defined in 2.4.3 Effective Boolean Value.
The following expression illustrates how a where
clause might be applied to a positional variable in order to perform sampling on an input sequence. This expression approximates the average value in a sequence by sampling one value out of each one hundred input values.
fn:avg(for $x at $i in $inputvalues
where $i mod 100 = 0
return $x)
The return
clause of a FLWOR expression is evaluated once for each tuple in the tuple stream, and the results of these evaluations are concatenated, as if by the comma operator, to form the result of the FLWOR expression.
If no order by
clause is present, the order of the tuple stream is determined by the for
and let
clauses and by ordering mode. If an order by
clause is present, it reorders the tuples in the tuple stream into a new, value-based order. In either case, the resulting order determines the order in which the return
clause is evaluated, once for each tuple, using the variable bindings in the
respective tuples. Note that ordering mode has no effect on a FLWOR expression if an order by
clause is present, since order by
takes precedence over ordering mode.
An order by
clause contains one or more ordering specifications, called orderspecs, as shown in the grammar above. For each tuple in the tuple stream, the orderspecs are evaluated, using the variable bindings in that tuple. The relative order of two tuples is determined by comparing the values of their orderspecs, working from left to right until a pair of unequal values is encountered. If the values to be compared are strings, the orderspec may indicate
the collation to be used (if no collation is specified, the default collation is used.)
The process of evaluating and comparing the orderspecs is based on the following rules:
Atomization is applied to the result of the expression in each orderspec. If the result of atomization is neither a single atomic value nor an empty sequence, a type error is raised.[err:XP0004][err:XP0006]
If the value of an orderspec has the dynamic type xdt:untypedAtomic
(such as character data in a schemaless document), it is cast to the type xs:string
.
Note:
Consistently treating untyped values as strings enables the sorting process to begin without complete knowledge of the types of all the values to be sorted.
All the non-empty orderspec values must be convertible to a common type by subtype substitution and/or numeric type promotion. The ordering is performed in the least common type that has a gt
operator. If two or more non-empty orderspec values are not convertible to a common type that has a gt
operator, a type error is raised. [err:XP0004][err:XP0006]
Example: The orderspec values include a value of type hatsize
, which is derived from xs:integer
, and a value of type shoesize
, which is derived from xs:decimal
. The least common type reachable by subtype substitution and numeric type promotion is xs:decimal
.
Example: The orderspec values include a value of type xs:string
and a value of type xs:anyURI
. Since these types have no common type reachable by subtype substitution and numeric type promotion, a type error is raised.
When two orderspec values are compared to determine their relative position in the ordering sequence, the greater-than relationship is defined as follows:
When the orderspec specifies empty least
, a value W is considered to be greater-than a value V if one of the following is true:
V is an empty sequence and W is not an empty sequence.
V is NaN
, and W is neither NaN
nor an empty sequence.
No collation is specified, and W gt
V is true.
A specific collation C is specified, and fn:compare(V, W, C)
is less than zero.
When the orderspec specifies empty greatest
, a value W is considered to be greater-than a value V if one of the following is true:
W is an empty sequence and V is not an empty sequence.
W is NaN
, and V is neither NaN
nor an empty sequence.
No collation is specified, and W gt
V is true.
A specific collation C is specified, and fn:compare(V, W, C)
is less than zero.
When the orderspec specifies neither empty least
nor empty greatest
, the default ordering for empty sequences in the static context determines whether the rules for empty least
or empty greatest
are used.
If T1 and T2 are two tuples in the tuple stream, and V1 and V2 are the first pair of values encountered when evaluating their orderspecs from left to right for which one value is greater-than the other (as defined above), then:
If V1 is greater-than V2: If the orderspec specifies descending
, then T1 precedes T2 in the tuple stream; otherwise, T2 precedes T1 in the tuple stream.
If V2 is greater-than V1: If the orderspec specifies descending
, then T2 precedes T1 in the tuple stream; otherwise, T1 precedes T2 in the tuple stream.
If neither V1 nor V2 is greater-than the other for any pair of orderspecs for tuples T1 and T2, then:
If stable
is specified, the original order of T1 and T2 is preserved in the tuple stream.
If stable
is not specified, the order of T1 and T2 in the tuple stream is implementation-dependent.
An order by
clause makes it easy to sort the result of a FLWOR expression, even if the sort key is not included in the result of the expression. For example, the following expression returns employee names in descending order by salary, without returning the actual salaries:
for $e in $employees
order by $e/salary descending
return $e/name
Note:
Since the order by
clause in a FLWOR expression is the only facility provided by XQuery for specifying a value ordering, a FLWOR expression must be used in some queries where iteration would not otherwise be necessary. For example, a list of books with price less than 100 might be obtained by a simple path expression such as $books/book[price < 100]
. But if these books are to be returned in alphabetic order by title, the query must be expressed as follows:
for $b in $books/book[price < 100]
order by $b/title
return $b
The following example illustrates an order by
clause that uses several options. It causes a collection of books to be sorted in primary order by title, and in secondary descending order by price. A specific collation is specified for the title ordering, and in the ordering by price, books with no price are specified to occur last (as though they have the least possible price). Whenever two books with the same title and price occur, the keyword
stable
indicates that their input order is preserved.
for $b in $books/book
stable order by $b/title
collation "http://www.example.org/collations/fr-ca",
$b/price descending empty least
return $b
The following example illustrates how FLWOR expressions can be nested, and how ordering can be specified at multiple levels of an element hierarchy. The example query inverts a document hierarchy to transform a bibliography into an author list. The input (bound to the variable $bib
) is a bib
element containing a list of books, each of which in turn contains a list of authors. The example is based on the following input:
<bib> <book> <title>TCP/IP Illustrated</title> <author>Stevens</author> <publisher>Addison-Wesley</publisher> </book> <book> <title>Advanced Programming in the Unix Environment</title> <author>Stevens</author> <publisher>Addison-Wesley</publisher> </book> <book> <title>Data on the Web</title> <author>Abiteboul</author> <author>Buneman</author> <author>Suciu</author> </book> </bib>
The following query transforms the input document into a list in which each author's name appears only once, followed by a list of titles of books written by that author. The fn:distinct-values
function is used to eliminate duplicates (by value) from a list of author nodes. The author list, and the lists of books published by each author, are returned in alphabetic order using the default collation.
<authlist>
{
for $a in fn:distinct-values($bib/book/author)
order by $a
return
<author>
<name> {$a} </name>
<books>
{
for $b in $bib/book[author = $a]
order by $b/title
return $b/title
}
</books>
</author>
}
</authlist>
The result of the above expression is as follows:
<authlist> <author> <name>Abiteboul</name> <books> <title>Data on the Web</title> </books> </author> <author> <name>Buneman</name> <books> <title>Data on the Web</title> </books> </author> <author> <name>Stevens</name> <books> <title>TCP/IP Illustrated</title> <title>Advanced Programming in the Unix Environment</title> </books> </author> <author> <name>Suciu</name> <books> <title>Data on the Web</title> </books> </author> </authlist>
[83] | OrderedExpr |
::= | "ordered" "{" Expr "}" |
[84] | UnorderedExpr |
::= | "unordered" "{" Expr "}" |
The purpose of ordered
and unordered
expressions is to set the ordering mode in the static context to ordered
or unordered
for a certain region in a query. The specified ordering mode applies to the expression nested inside the curly braces. For expressions where the ordering of the result is not significant, a performance advantage may be
realized by setting the ordering mode to unordered
, thereby granting the system flexibility to return the result in the order that it finds most efficient.
Ordering mode affects the behavior of path expressions, union
, intersect
, and except
expressions, and FLWOR expressions that have no order by
clause. If ordering mode is ordered
, node sequences returned by path, union
, intersect
, and except
expressions are in document order; otherwise the
order of these return sequences is implementation-dependent. The effect of ordering mode on FLWOR expressions is described in 3.8 FLWOR Expressions. Ordering mode has no effect on duplicate elimination.
Note:
In a region of the query where ordering mode is unordered
, certain functions that depend on the ordering of node sequences may return nondeterministic results. These functions include fn:position
, fn:last
, fn:index-of
, fn:insert-before
, fn:remove
, fn:reverse
, and fn:subsequence
. Also, within a path expression in an unordered region, numeric
predicates are nondeterministic. For example, in an ordered region, the path expression //a/b[5]
will return the fifth qualifying b
-element in document order. In an unordered region, the same expression will return an implementation-dependent qualifying b
-element.
The use of an unordered
expression is illustrated by the following example, which joins together two documents named parts.xml
and suppliers.xml
. The example returns the part numbers of red parts, paired with the supplier numbers of suppliers who supply these parts. If an unordered
expression were not used, the resulting list of (part number, supplier number) pairs would be required to have an ordering that is controlled primarily by the document order of parts.xml
and secondarily by the document order of suppliers.xml
. However, this might not be the most efficient way to process the query if the ordering of the result is not important. An XQuery implementation might be able to process the query more efficiently by using an index to find the red parts, or by using suppliers.xml
rather than
parts.xml
to control the primary ordering of the result. The unordered
expression gives the query evaluator freedom to make these kinds of optimizations.
unordered {
for $p in fn:doc("parts.xml")/parts/part[color = "Red"],
$s in fn:doc("suppliers.xml")/suppliers/supplier
where $p/suppno = $s/suppno
return
<ps>
{ $p/partno, $s/suppno }
</ps>
}
In addition to ordered
and unordered
expressions, XQuery provides a function named fn:unordered
that operates on any sequence of items and returns the same sequence in a nondeterministic order. A call to the fn:unordered
function may be thought of as giving permission for the argument expression to be materialized in whatever order the system finds most efficient. The fn:unordered
function differs from an unordered
expression
in the following ways:
The fn:unordered
function relaxes ordering only for the sequence that is its immediate operand, whereas an unordered
expression sets the ordering mode for its operand expression and all nested expressions.
The fn:unordered
function can operate on any sequence, whereas an unordered
expression affects the ordering only of node sequences (not sequences of atomic values).
XQuery supports a conditional expression based on the keywords if
, then
, and else
.
[42] | IfExpr |
::= | "if" "(" Expr ")" "then" ExprSingle "else" ExprSingle |
The expression following the if
keyword is called the test expression, and the expressions following the then
and else
keywords are called the then-expression and else-expression, respectively.
The first step in processing a conditional expression is to find the effective boolean value of the test expression, as defined in 2.4.3 Effective Boolean Value.
The value of a conditional expression is defined as follows: If the effective boolean value of the test expression is true
, the value of the then-expression is returned. If the effective boolean value of the test expression is false
, the value of the else-expression is returned.
Conditional expressions have a special rule for propagating dynamic errors. If the effective value of the test expression is true
, the conditional expression ignores (does not raise) any dynamic errors encountered in the else-expression. In this case, since the else-expression can have no observable effect, it need not be evaluated. Similarly, if the effective value of the test expression is false
, the conditional expression
ignores any dynamic errors encountered in the then-expression, and the then-expression need not be evaluated.
Here are some examples of conditional expressions:
In this example, the test expression is a comparison expression:
if ($widget1/unit-cost < $widget2/unit-cost) then $widget1 else $widget2
In this example, the test expression tests for the existence of an attribute named discounted
, independently of its value:
if ($part/@discounted) then $part/wholesale else $part/retail
Quantified expressions support existential and universal quantification. The value of a quantified expression is always true
or false
.
[39] | QuantifiedExpr |
::= | (("some" "$") | ("every" "$")) VarName TypeDeclaration? "in" ExprSingle ("," "$" VarName TypeDeclaration? "in" ExprSingle)* "satisfies" ExprSingle |
A quantified expression begins with a quantifier, which is the keyword some
or every
, followed by one or more in-clauses that are used to bind variables, followed by the keyword satisfies
and a test expression. Each in-clause associates a variable with an expression that returns a sequence of items, called the binding sequence for that variable. The in-clauses generate tuples of variable bindings, including a tuple for each combination of items
in the binding sequences of the respective variables. Conceptually, the test expression is evaluated for each tuple of variable bindings. Results depend on the effective boolean value of the test expressions, as defined in 2.4.3 Effective Boolean Value. The value of the quantified expression is defined by the following rules:
If the quantifier is some
, the quantified expression is true
if at least one evaluation of the test expression has the effective boolean value true
; otherwise the quantified expression is false
. This rule implies that, if the in-clauses generate zero binding tuples, the value of the quantified expression is false
.
If the quantifier is every
, the quantified expression is true
if every evaluation of the test expression has the effective boolean value true
; otherwise the quantified expression is false
. This rule implies that, if the in-clauses generate zero binding tuples, the value of the quantified expression is true
.
The scope of a variable bound in a quantified expression comprises all subexpressions of the quantified expression that appear after the variable binding. The scope does not include the expression to which the variable is bound.
Each variable bound in an in-clause of a quantified expression may have an optional type declaration, which is a datatype declared using the syntax in 2.5.4 SequenceType Matching. If the type of a value bound to the variable does not match the declared type according to the rules for SequenceType matching, a type error is raised.[err:XP0004][err:XP0006]
The order in which test expressions are evaluated for the various binding tuples is implementation-dependent. If the quantifier is some
, an implementation may return true
as soon as it finds one binding tuple for which the test expression has an effective boolean value of true
, and it may raise a dynamic error as soon as it finds one binding tuple for which the test expression raises an error. Similarly, if the quantifier is every
, an implementation may return false
as soon as it finds one binding tuple for which the test expression has an effective boolean value of false
, and it may raise a dynamic error as soon as it finds one
binding tuple for which the test expression raises an error. As a result of these rules, the value of a quantified expression is not deterministic in the presence of errors, as illustrated in the examples below.
Here are some examples of quantified expressions:
This expression is true
if every part
element has a discounted
attribute (regardless of the values of these attributes):
every $part in /parts/part satisfies $part/@discounted
This expression is true
if at least one employee
element satisfies the given comparison expression:
some $emp in /emps/employee satisfies ($emp/bonus > 0.25 * $emp/salary)
In the following examples, each quantified expression evaluates its test expression over nine tuples of variable bindings, formed from the Cartesian product of the sequences (1, 2, 3)
and (2, 3, 4)
. The expression beginning with some
evaluates to true
, and the expression beginning with every
evaluates to false
.
some $x in (1, 2, 3), $y in (2, 3, 4)
satisfies $x + $y = 4
every $x in (1, 2, 3), $y in (2, 3, 4)
satisfies $x + $y = 4
This quantified expression may either return true
or raise a type error, since its test expression returns true
for one variable binding and raises a type error for another:
some $x in (1, 2, "cat") satisfies $x * 2 = 4
This quantified expression may either return false
or raise a type error, since its test expression returns false
for one variable binding and raises a type error for another:
every $x in (1, 2, "cat") satisfies $x * 2 = 4
This quantified expression contains a type declaration that is not satisfied by every item in the test expression. If the Static Typing Feature is implemented, this expression raises a type error during the analysis phase. Otherwise, the expression may either return true
or raise a type error during the evaluation
phase.
some $x as xs:integer in (1, 2, "cat") satisfies $x * 2 = 4
In addition to their use in function parameters and results, SequenceTypes are used in instance of
, typeswitch
, cast
, castable
, and treat
expressions.
[51] | InstanceofExpr |
::= | TreatExpr ( "instance" "of" SequenceType )? |
The boolean operator instance of
returns true
if the value of its first operand matches the SequenceType in its second operand, according to the rules for SequenceType matching; otherwise it returns false
. For example:
5 instance of xs:integer
This example returns true
because the given value is an instance of the given type.
5 instance of xs:decimal
This example returns true
because the given value is an integer literal, and xs:integer
is derived by restriction from xs:decimal
.
<a>{5}</a> instance of xs:integer
This example returns false
because the given value is an element rather than an integer.
. instance of element()
This example returns true
if the context item is an element node or false
if the context item is defined but is not an element node. If the context item is undefined, a dynamic error is raised.[err:XP0002]
[40] | TypeswitchExpr |
::= | "typeswitch" "(" Expr ")" CaseClause+ "default" ("$" VarName)? "return" ExprSingle |
[41] | CaseClause |
::= | "case" ("$" VarName "as")? SequenceType "return" ExprSingle |
The typeswitch expression chooses one of several expressions to evaluate based on the dynamic type of an input value.
In a typeswitch
expression, the typeswitch
keyword is followed by an expression enclosed in parentheses, called the operand expression. This is the expression whose type is being tested. The remainder of the typeswitch
expression consists of one or more case
clauses and a default
clause.
Each case
clause specifies a SequenceType followed by a return
expression. [Definition: The effective case in a typeswitch
expression is the first case
clause such that the value of the operand expression matches the SequenceType in the case
clause, using the rules of SequenceType matching.] The value of the typeswitch
expression is the value of the return
expression in the effective case. If the value of the operand expression does not match any type named in a case
clause, the value of the typeswitch
expression is the value of the return
expression in the default
clause.
In a case
or default
clause, if the value to be returned depends on the value of the operand expression, the clause must specify a variable name. Within the return
expression of the case
or default
clause, this variable name is bound to the value of the operand expression. Inside a case
clause, the static type of the variable is the SequenceType named in the case
clause. Inside a default
clause, the static type of the variable is the same as the static type of the operand expression. If the value to be returned by a case
or default
clause does not depend on the value of the operand expression, the clause need not specify a variable.
The scope of a variable binding in a case
or default
clause comprises that clause. It is not an error for more than one case
or default
clause in the same typeswitch
expression to bind variables with the same name.
A special rule applies to propagation of dynamic errors by typeswitch
expressions. A typeswitch
expression ignores (does not raise) any dynamic errors encountered in case
clauses other than the effective case. Dynamic errors encountered in the default
clause are raised only if there is no effective case.
The following example shows how a typeswitch
expression might be used to process an expression in a way that depends on its dynamic type.
typeswitch($customer/billing-address)
case $a as element(*, USAddress) return $a/state
case $a as element(*, CanadaAddress) return $a/province
case $a as element(*, JapanAddress) return $a/prefecture
default return "unknown"
[54] | CastExpr |
::= | UnaryExpr ( "cast" "as" SingleType )? |
[109] | SingleType |
::= | AtomicType "?"? |
Occasionally it is necessary to convert a value to a specific datatype. For this purpose, XQuery provides a cast
expression that creates a new value of a specific type based on an existing value. A cast
expression takes two operands: an input expression and a target type. The type of the input expression is called the input type. The target type must be a named atomic type, represented by a QName, optionally followed by the occurrence indicator
?
if an empty sequence is permitted. If the target type has no namespace prefix, it is considered to be in the default element/type namespace. The semantics of the cast
expression are as follows:
Atomization is performed on the input expression.
If the result of atomization is a sequence of more than one atomic value, a type error is raised.[err:XP0004][err:XP0006]
If the result of atomization is an empty sequence:
If ?
is specified after the target type, the result of the cast
expression is an empty sequence.
If ?
is not specified after the target type, a type error is raised.[err:XP0004][err:XP0006]
If the result of atomization is a single atomic value, the result of the cast expression depends on the input type and the target type. In general, the cast expression attempts to create a new value of the target type based on the input value. Only certain combinations of input type and target type are supported. A summary of the rules are listed below— the normative definition of these rules is given in [XQuery 1.0 and XPath 2.0 Functions and Operators]. For the purpose of these rules, an implementation may determine that one type is derived by restriction from another type either by examining the in-scope schema definitions or by using an alternative, implementation-dependent mechanism such as a data dictionary.
cast
is supported for the combinations of input type and target type listed in [XQuery 1.0 and XPath 2.0 Functions and Operators]. For each of these combinations, both the input type and the target type are primitive schema types. For example, a value of type xs:string
can be cast into the type xs:decimal
. For each of these built-in combinations, the semantics of casting are specified in [XQuery
1.0 and XPath 2.0 Functions and Operators].
cast
is supported if the input type is a non-primitive atomic type that is derived by restriction from the target type. In this case, the input value is mapped into the value space of the target type, unchanged except for its type. For example, if shoesize
is derived by restriction from xs:integer
, a value of type shoesize
can be cast into the type xs:integer
.
cast
is supported if the target type is a non-primitive atomic type and the input type is xs:string
or xdt:untypedAtomic
. The input value is first converted to a value in the lexical space of the target type by applying the whitespace normalization rules for the target type; a dynamic error [err:XP0029] is raised if the resulting lexical value does not satisfy the
pattern facet of the target type. The lexical value is then converted to the value space of the target type using the schema-defined rules for the target type; a dynamic error[err:XP0029] is raised if the resulting value does not satisfy all the facets of the target type.
cast
is supported if the target type is a non-primitive atomic type that is derived by restriction from the input type. The input value must satisfy all the facets of the target type (in the case of the pattern facet, this is checked by generating a string representation of the input value, using the rules for casting to xs:string
). The resulting value is the same as the input value, but with a different dynamic type.
If a primitive type P1 can be cast into a primitive type P2, then any type derived by restriction from P1 can be cast into any type derived by restriction from P2, provided that the facets of the target type are satisfied. First the input value is cast to P1 using rule (b) above. Next, the value of type P1 is cast to the type P2, using rule (a) above. Finally, the value of type P2 is cast to the target type, using rule (d) above.
For any combination of input type and target type that is not in the above list, a cast
expression raises a type error.[err:XP0004][err:XP0006]
If casting from the input type to the target type is supported but nevertheless it is not possible to cast the input value into the value space of the target type, a dynamic error is raised.[err:XP0021] This includes the case when any facet of the target type is not satisfied. For example, the expression "2003-02-31" cast as xs:date
would raise a dynamic error.
[53] | CastableExpr |
::= | CastExpr ( "castable" "as" SingleType )? |
XQuery provides an expression that tests whether a given value is castable into a given target type. The expression V castable as T
returns true
if the value V
can be successfully cast into the target type T
by using a cast
expression; otherwise it returns false
. The castable
expression can be used as a predicate to avoid errors at evaluation time. It can also be used
to select an appropriate type for processing of a given value, as illustrated in the following example:
if ($x castable as hatsize) then $x cast as hatsize else if ($x castable as IQ) then $x cast as IQ else $x cast as xs:string
For every atomic type in the in-scope type definitions that is in a namespace, a constructor function is implicitly defined. In each case, the name of the constructor function is the same as the name of its target type (including namespace). The signature of the constructor function for type T is as follows:
T($arg as xdt:anyAtomicType?) as T?
Constructor functions are normatively defined in [XQuery 1.0 and XPath 2.0 Functions and Operators]. In general, if the argument to a constructor function is of type xs:string
, the string is whitespace-normalized and converted to the target type by schema validation; otherwise, the semantics of the constructor function are identical to $arg cast as T
.
The following examples illustrate the use of constructor functions:
This example is equivalent to "2000-01-01" cast as xs:date
.
xs:date("2000-01-01")
This example is equivalent to ($floatvalue * 0.2E-5) cast as xs:decimal
.
xs:decimal($floatvalue * 0.2E-5)
This example returns a xdt:dayTimeDuration
value equal to 21 days. It is equivalent to "P21D" cast as xdt:dayTimeDuration
.
xdt:dayTimeDuration("P21D")
If usa:zipcode
is a user-defined atomic type in the in-scope type definitions, then the following expression is equivalent to the expression "12345" cast as usa:zipcode
.
usa:zipcode("12345")
Atomic types that are not in a namespace do not have constructor functions. To construct an instance of such a type, it is necessary to use a cast
expression. For example, if the user-defined type apple
is derived from xs:integer
but is not in a namespace, an instance of this type can be constructed as follows (but only if the default element/type namespace is no namespace):
17 cast as apple
[52] | TreatExpr |
::= | CastableExpr ( "treat" "as" SequenceType )? |
XQuery provides an expression called treat
that can be used to modify the static type of its operand.
Like cast
, the treat
expression takes two operands: an expression and a SequenceType. Unlike cast
, however, treat
does not change the dynamic type or value of its operand. Instead, the purpose of treat
is to ensure that an expression has an expected dynamic type at evaluation time.
The semantics of expr1
treat as
type1
are as follows:
During static analysis:
The static type of the treat
expression is type1
. This enables the expression to be used as an argument of a function that requires a parameter of type1
.
During expression evaluation:
If expr1
matches type1
, using the rules for SequenceType matching, the treat
expression returns the value of expr1
; otherwise, it raises a dynamic error.[err:XP0050] If the value of expr1
is returned, its identity is preserved. The
treat
expression ensures that the value of its expression operand conforms to the expected type at run-time.
Example:
$myaddress treat as element(*, USAddress)
The static type of $myaddress
may be element(*, Address)
, a less specific type than element(*, USAddress)
. However, at run-time, the value of $myaddress
must match the type element(*, USAddress)
using rules for SequenceType matching; otherwise a dynamic error is
raised.[err:XP0050]
[60] | ValidateExpr |
::= | "validate" ValidationMode? "{" Expr "}" |
[138] | ValidationMode |
::= | "lax" | "strict" |
A validate
expression can be used to validate a document node or an element node with respect to the in-scope schema definitions, using the schema validation process defined in [XML Schema]. If the operand of a validate
expression does not evaluate to exactly one document or element node, a type error is raised.[err:XQ0030]
A validate
expression returns a new node with its own identity and with no parent. The new node and its descendants are given type annotations that are generated by applying a validation process to the operand node. In some cases, default values may also be generated by the validation process.
The validate
expression begins by making a new copy of the operand node, including all its properties (base-uri, in-scope namespaces, etc.), and including new copies of all its attributes and descendant nodes (if any). In the following description, the copy of the operand node is called the candidate node, and the term contained nodes means the element and attribute nodes that have the candidate node as an ancestor. The candidate node is processed according to the following
rules, and is then returned as the result of the validate
expression.
If the candidate node is an element node, the result of the validate expression is defined by the following rules.
If ValidationMode is strict
or is not specified, schema validity assessment is performed on the candidate node as follows:
The candidate node is converted to an XML Information Set ([XML Infoset]) according to the "Infoset Mapping" rules defined in [XQuery 1.0 and XPath 2.0 Data Model]. Note that this process discards any existing type annotations.
The resulting Information Set is validated as follows:
Validity assessment is carried out on the root element information item, according to the rules in [XML Schema] Part 1, Section 3.3.4, "Schema-Validity Assessment (Element)", using the in-scope schema definitions as the effective schema. The process of validation applies recursively to contained elements and attributes to the extent required by the effective schema. Note that the validity assessment process is affected
by the presence or absence of an xsi:type
attribute on the candidate node, and may generate new information items such as default attributes.
During validity assessment, the following special rules are in effect:
The validation rule "Validation Root Valid (ID/IDREF)" is not applied. This means that validation will not fail if there are non-unique ID
values or dangling IDREF
values in the subtree being validated.
The validation rule "Validation Rule: Identity-constraint Satisfied" is not applied.
There is no check that the document contains unparsed entities whose names match the values of nodes of type xs:ENTITY
or xs:ENTITIES
.
There is no check that the document contains notations whose names match the values of nodes of type xs:NOTATION
.
If the result of schema validity assessment is a PSVI in which the root element information item has the validity property valid
, this PSVI is converted back into the Data Model by the process described in [XQuery 1.0 and XPath 2.0 Data Model] Section 3.3, "Construction from a PSVI", replacing the candidate node. Otherwise, a dynamic error is raised. [err:XQ0027] In effect this means that the candidate node must have a top-level element declaration in the effective schema, and must conform to this declaration.
If ValidationMode is lax
, the candidate node is processed as though ValidationMode were strict
, with the following exception: Whereas strict
validation fails if the outcome of validity assessment is a validity property of invalid
or notKnown
, lax
validation fails only if the outcome of validity assessment is a validity property of
invalid
. That is, lax
validation does not raise an error when the outcome is notKnown
.
In practice this means that the candidate node must conform to its top-level declaration if such a declaration exists in the effective schema. If no such declaration exists, then the candidate node is not validated, but its attributes and children are validated, again with lax
validation. After validation, elements whose validity property is notKnown
are represented in the Data Model as element nodes with type xs:anyType
. Attributes whose validity property is
notKnown
are represented in the Data Model as attribute nodes with type xdt:untypedAtomic
.
If the candidate node of a validate
expression is a document node, the result of the validate
expression is defined by the following rules.
A dynamic error [err:XQ0061] is raised if the children of the candidate node do not consist of exactly one element node and zero or more comment and processing instruction nodes, in any order.
The single element node child is converted to an Infoset and validated, as described in 3.13.1 Validating an Element Node, with the following special rules:
The validation rule "Validation Root Valid (ID/IDREF)" is applied. A dynamic error [err:XQ0062] is raised if non-unique ID values or dangling IDREF values are found in the document tree.
Identity constraints, as defined in section 3.11 of [XML Schema] Part 1, are checked. (This refers to constraints defined using xs:unique
, xs:key
, and xs:keyref
.) A dynamic error [err:XQ0062] is raised if an identity constraint is found to be violated.
The next step depends on the validity
property of the root information item in the PSVI that results from the validation process. If this property is valid
, the PSVI is converted back into the Data Model as described in [XQuery 1.0 and XPath 2.0 Data Model] Section 3.3, "Construction from a PSVI". The resulting node hierarchy replaces the original element child of the candidate node, taking its place among other descendants of the candidate node, which
remain unchanged. Otherwise, a dynamic error is raised. [err:XQ0027]
[1] | Module |
::= | VersionDecl? (MainModule | LibraryModule) |
[3] | MainModule |
::= | Prolog QueryBody |
[4] | LibraryModule |
::= | ModuleDecl Prolog |
[6] | Prolog |
::= | (Setter Separator)* ((Import | NamespaceDecl | DefaultNamespaceDecl) Separator)* ((VarDecl | FunctionDecl) Separator)* |
[7] | Setter |
::= | XMLSpaceDecl | DefaultCollationDecl | BaseURIDecl | ConstructionDecl | OrderingModeDecl | EmptyOrderingDecl | InheritNamespacesDecl |
[8] | Import |
::= | SchemaImport | ModuleImport |
[9] | Separator |
::= | ";" |
[27] | QueryBody |
::= | Expr |
A query can be assembled from one or more fragments called modules. [Definition: A module is a fragment of XQuery code that conforms to the Module grammar and can independently undergo the static analysis phase described in 2.2.3 Expression Processing. Each module is either a main module or a library module.]
[Definition: A main module consists of a Prolog followed by a Query Body.] A query has exactly one main module. In a main module, the Query Body can be evaluated, and its value is the result of the query.
[Definition: A module that does not contain a Query Body is called a library module. A library module consists of a module declaration followed by a Prolog.] A library module cannot be evaluated directly; instead, it provides function and variable declarations that can be imported into other modules.
The XQuery syntax does not allow a module to contain both a module declaration and a Query Body.
[Definition: A Prolog is a series of declarations and imports that define the processing environment for the module that contains the Prolog.] Each declaration or import is followed by a semicolon. [Definition: The first part of the Prolog consists of declarations that are called setters because they set the value of some property that affects query processing, such as construction mode, ordering mode, or default collation.] The setters are followed by declarations of namespaces and default namespaces and by imports of schemas and modules. [Definition: Each imported schema or module is identified by its target namespace, which is the namespace of the objects (such as elements or functions) that are defined by the schema or module.] The final part of the Prolog consists of declarations of variables and functions.
[Definition: The Query Body, if present, consists of an expression that defines the result of the query.] Evaluation of expressions is described in 3 Expressions. A module can be evaluated only if it has a Query Body.
[2] | VersionDecl |
::= | "xquery" "version" StringLiteral ("encoding" StringLiteral)? Separator |
[Definition: Any module may contain a version declaration. If present, the version declaration occurs at the beginning of the module and identifies the applicable XQuery syntax and semantics for the module.] The version number "1.0" indicates a requirement that the module must be processed by an implementation that supports XQuery Version 1.0. If the version declaration is not present, the version is presumed to be "1.0". An XQuery implementation must raise a static error [err:XQ0031] when processing a module labeled with a version that the implementation does not support. It is the intent of the XQuery working group to give later versions of this specification numbers other than "1.0", but this intent does not indicate a commitment to produce any future versions of XQuery, nor if any are produced, to use any particular numbering scheme.
[Definition: If present, a version declaration may optionally include an encoding declaration. The purpose of an encoding declaration is to allow the writer of a query to provide a string that indicates how the query is encoded, such as "utf-8
", "utf-16
", or "us-ascii
".] Since the encoding of a query may change as the query moves from one environment to another,
there can be no guarantee that the encoding declaration is correct. The semantics of a query are not affected by the presence or absence of an encoding declaration.
The following examples illustrate version declarations:
xquery version "1.0";
xquery version "1.0" encoding "utf-8";
[5] | ModuleDecl |
::= | "module" "namespace" NCName "=" StringLiteral Separator |
[Definition: A module declaration serves to identify a module as a library module. A module declaration consists of the keyword module
followed by a namespace prefix and a string literal which must contain a valid URI. [err:XQ0046]] The URI identifies the
target namespace of the library module, which is the namespace for all variables and functions exported by the library module. The name of every variable and function declared in a library module must have a namespace URI that is the same as the target namespace of the module; otherwise a static error is raised. [err:XQ0048]
Any module may import one or more library modules by means of a module import that specifies the target namespace of the library modules to be imported. When a module imports one or more library modules, the variables and functions declared in the imported modules are added to the static context and (where applicable) to the dynamic context of the importing module.
The following is an example of a module declaration:
module namespace math = "http://example.org/math-functions";
[11] | XMLSpaceDecl |
::= | "declare" "xmlspace" ("preserve" | "strip") |
[Definition: An xmlspace declaration sets the XMLSpace policy in the static context, overriding any implementation-provided default. XMLSpace policy controls whether boundary whitespace is preserved by element constructors during processing of
the query.] If XMLSpace policy is preserve
, boundary whitespace is preserved. If XMLSpace policy is strip
, boundary whitespace is stripped (deleted). A further discussion of whitespace in constructed elements can be found in 3.7.1.4 Whitespace in Element Content.
The following example illustrates an xmlspace declaration:
declare xmlspace preserve;
If a Prolog contains more than one Xmlspace declaration, a static error is raised.[err:XQ0038]
[16] | DefaultCollationDecl |
::= | "declare" "default" "collation" StringLiteral |
[Definition: A default collation declaration sets the value of the default collation in the static context, overriding any implementation-provided default.] The default collation is the collation that is used by functions and operators that require a collation if no other
collation is specified. For example, the gt
operator on strings is defined by a call to the fn:compare
function, which takes an optional collation parameter. Since the gt
operator does not specify a collation, the fn:compare
function implements gt
by using the default collation. A default collation declaration specifies the default collation by a literal string which must contain a valid URI. [err:XQ0046]
If neither the implementation nor the Prolog specifies a default collation, the Unicode codepoint collation (http://www.w3.org/2004/10/xpath-functions/collation/codepoint
) is used.
The following example illustrates a default collation declaration:
declare default collation "http://example.org/languages/Icelandic";
If a Prolog contains more than one default collation declaration, or the value specified does not identify a collation known to the implementation, a static error is raised.[err:XQ0038]
[17] | BaseURIDecl |
::= | "declare" "base-uri" StringLiteral |
[Definition: A base URI declaration specifies the base URI property of the static context, which is used when resolving relative URIs within a module.] A static error [err:XQ0046] is
raised if the string literal in a base URI declaration does not contain a valid URI. Note that the fn:doc
function resolves a relative URI using the base URI of the calling module.
The following is an example of a base URI declaration:
declare base-uri "http://example.org";
If a Prolog contains more than one base URI declaration, a static error is raised. [err:XQ0032]
[22] | ConstructionDecl |
::= | "declare" "construction" ("preserve" | "strip") |
[Definition: A construction declaration sets the construction mode in the static context, overriding any implementation-provided default.] The construction mode governs the behavior of element constructors. If construction mode is preserve
, the type of a constructed element
node is xs:anyType
, and the attributes and descendants of the constructed element retain their original types. If construction mode is strip
, the type of the constructed element node and all its descendants is xdt:untyped
, and attributes of the constructed element have type xdt:untypedAtomic
. Element constructors are described in 3.7.1 Direct Element Constructors and 3.7.3.1
Computed Element Constructors.
The following example illustrates a construction declaration:
declare construction strip;
If a Prolog specifies more than one construction declaration, a static error is raised.[err:XQ0067]
[13] | OrderingModeDecl |
::= | "declare" "ordering" ("ordered" | "unordered") |
[Definition: An ordering mode declaration sets the ordering mode in the static context, overriding any implementation-defined default.] This ordering mode applies to all expressions in a module (including both the Prolog and the Query Body, if any), unless overridden by an ordered
or unordered
expression.
Ordering mode affects the behavior of path expressions, union
, intersect
, and except
expressions, and FLWOR expressions that have no order by
clause. If ordering mode is ordered
, node sequences returned by path, union
, intersect
, and except
expressions are in document order; otherwise the
order of these return sequences is implementation-dependent. The effect of ordering mode on FLWOR expressions is described in 3.8 FLWOR Expressions.
The following example illustrates an ordering mode declaration:
declare ordering unordered;
If a Prolog contains more than one ordering mode declaration, a static error is raised. [err:XQ0065]
[14] | EmptyOrderingDecl |
::= | "declare" "default" "order" ("empty" "greatest" | "empty" "least") |
[Definition: An empty ordering declaration sets the default ordering for empty sequences in the static context, which controls whether an empty sequence is interpreted as the greatest value or as the least value during processing of an order by
clause in a FLWOR expression.] An individual order by
clause may override the default ordering for empty sequences by specifying empty greatest
or empty least
.
The following example illustrates an empty ordering declaration:
declare default ordering empty least;
If a Prolog contains more than one empty ordering declaration, a static error is raised. [err:XQ0055]
Note:
It is important to distinguish an empty ordering declaration from an ordering mode declaration. An empty ordering declaration applies only when an order by
clause is present, and specifies how empty sequences are treated by the order by
clause (unless overridden).
An ordering mode declaration, on the other hand, applies only in the absence of an order by
clause.
[15] | InheritNamespacesDecl |
::= | "declare" "inherit-namespaces" ("yes" | "no") |
[Definition: An inherit-namespaces declaration sets the value of namespace inheritance mode in the static context, overwriting any implementation-provided default. Namespace inheritance mode controls the namespace bindings that are inherited when an existing element node is copied by an element constructor.] Copying of namespace bindings by element constructors is described in 3.7.1 Direct Element Constructors.
The following example illustrates an inherit-namespaces declaration:
declare inherit-namespaces no;
If a Prolog contains more than one inherit-namespaces declaration, a static error is raised. [err:XQ0055]
[18] | SchemaImport |
::= | "import" "schema" SchemaPrefix? StringLiteral (("at" StringLiteral) ("," StringLiteral)*)? |
[19] | SchemaPrefix |
::= | ("namespace" NCName "=") | ("default" "element" "namespace") |
[Definition: A schema import imports the element, attribute, and type definitions from a schema into the in-scope schema definitions.] The schema to be imported is identified by its target namespace. The schema import may bind a namespace prefix to the target namespace of the imported schema, or may declare that target namespace to be the default element/type namespace. The schema import may also provide optional hints for locating the schema.
The string literals in a schema import must be valid URIs. [err:XQ0046] The first of these string literals specifies the target namespace of the schema to be imported. The string literals that follow the at
keyword are optional location hints, and can be interpreted or disregarded in an implementation-dependent way. Multiple location hints might be used to indicate more than one possible place to look for the schema or multiple physical resources
to be assembled to form the schema.
A schema import that specifies a zero-length string as target namespace is considered to import a schema that has no target namespace. Such a schema import may not bind a namespace prefix [err:XQ0057], but it may set the default element/type namespace to "no namespace", enabling the definitions in the imported namespace to be referenced. If the default element/type namespace is not set to "no namespace", there is no way to reference the definitions in an imported schema that has no target namespace.
It is a static error [err:XQ0058] if more than one schema import in the same Prolog specifies the same target namespace. It is a static error [err:XQ0059] if the implementation is not able to process a schema import by finding a valid schema with the specified target
namespace. It is a static error [err:XQ0035] if multiple imported schemas, or multiple physical resorces within one schema, contain definitions for the same name in the same symbol space (for example, two definitions for the same element name, even if the definitions are consistent). However, it is not an error to import the schema with target namespace http://www.w3.org/2001/XMLSchema
(predeclared
prefix xs
), even though the built-in types defined in this schema are implicitly included in the in-scope type definitions.
The following example imports a schema, specifying both its target namespace and its location, and binding the prefix soap
to the target namespace:
import schema namespace soap="http://www.w3.org/2003/05/soap-envelope" at "http://www.w3.org/2003/05/soap-envelope/";
The following example imports a schema by specifying only its target namespace, and makes it the default element/type namespace:
import schema default element namespace "http://example.org/abc";
The following example imports a schema that has no target namespace, providing a location hint, and sets the default element/type namespace to "no namespace" so that the definitions in the imported schema can be referenced:
import schema default element namespace "" at "http://example.org/xyz.xsd";
The following example imports a schema that has no target namespace and sets the default element/type namespace to "no namespace". Since no location hint is provided, it is up to the implementation to find the schema to be imported.
import schema default element namespace "";
[20] | ModuleImport |
::= | "import" "module" ("namespace" NCName "=")? StringLiteral (("at" StringLiteral) ("," StringLiteral)*)? |
[Definition: A module import imports the function declarations and variable declarations from one or more library modules into the function signatures and in-scope variables of the importing module.] Each module import names a target namespace, and imports all the modules that share this target namespace. The module import may bind a namespace prefix to the target namespace, and it may provide optional hints for locating the modules to be imported.
The string literals in a module import must be valid URIs. [err:XQ0046] The first of these string literals specifies the target namespace of the modules to be imported. The string literals that follow the at
keyword are optional location hints, and can be interpreted or disregarded in an implementation-defined way.
It is a static error [err:XQ0047] if more than one module import in a Prolog specifies the same target namespace. It is a static error [err:XQ0056] if the target namespace of the modules to be imported is the same as the target namespace of the importing module. It is a static error [err:XQ0059] if the implementation is not able to process a module import by finding a valid module definition with the specified target namespace. It is a static error if the name and arity of a function declared in an imported module is the same as the name and arity of a function declared in the importing module or in another imported module (even if the declarations are consistent). [err:XQ0034] It is a static error if the expanded QName of a variable declared in an imported module is the same as the expanded QName of a variable declared in the importing module or in another imported module (even if the declarations are consistent). [err:XQ0049]
Each module has its own static context. A module import imports only functions and variable declarations; it does not import other objects from the imported modules, such as in-scope schema definitions or statically known namespaces. Module imports are not transitive—that is, importing a module provides access only to function and variable declarations contained directly in the imported module. For example, if module A imports module B, and module B imports module C, module A does not have access to the functions and variables declared in module C. Nevertheless, it is a static error [err:XQ0073] if the graph of module imports contains a cycle (that is, if there exists a sequence of modules M1 ... Mn such that each Mi imports Mi+1 and Mn imports M1.)
It is a type error [err:XQ0036] to import a module if the importing module's in-scope type definitions do not include definitions for the type names that appear in variable declarations, function parameters, or function returns found in the imported module.
To illustrate the above rules, suppose that a certain schema defines a type named triangle
. Suppose that a library module imports the schema, binds its target namespace to the prefix geometry
, and declares a function with the following function signature: math:area($t as geometry:triangle) as xs:double
. If a query wishes to use this function, it must import both the library module and the
schema on which it is based. Importing the library module alone would not provide access to the definition of the type geometry:triangle
used in the signature of the area
function.
The following example illustrates a module import:
import module namespace math = "http://example.org/math-functions";
[10] | NamespaceDecl |
::= | "declare" "namespace" NCName "=" StringLiteral |
[Definition: A namespace declaration declares a namespace prefix and associates it with a namespace URI, adding the (prefix, URI) pair to the set of statically known namespaces.] The string literal used in a namespace declaration must be a valid URI [err:XQ0046] or a zero-length string. The namespace declaration is in scope throughout the query in which it is declared, unless it is overridden by a namespace declaration attribute in a direct element constructor.
The following query illustrates a namespace declaration:
declare namespace foo = "http://example.org"; <foo:bar> Lentils </foo:bar>
In the query result, the newly created node is in the namespace associated with the namespace URI http://example.org
.
Multiple declarations of the same namespace prefix in a Prolog result in a static error.[err:XQ0033]
It is a static error [err:XP0008] if an expression contains a QName with a namespace prefix that is not in the statically known namespaces.
XQuery has several predeclared namespace prefixes that are present in the statically known namespaces before each query is processed. These prefixes may be used without an explicit declaration. They may be overridden by namespace declarations in a Prolog or by namespace declaration attributes on constructed elements (except for the prefix xml
, which may not be redeclared [err:XQ0070]). The predeclared namespace prefixes are as follows:
xml = http://www.w3.org/XML/1998/namespace
xs = http://www.w3.org/2001/XMLSchema
xsi = http://www.w3.org/2001/XMLSchema-instance
fn = http://www.w3.org/2004/10/xpath-functions
xdt = http://www.w3.org/2004/10/xpath-datatypes
local = http://www.w3.org/2004/10/xquery-local-functions
(see 4.15 Function Declaration.)
Additional predeclared namespace prefixes may be added to the statically known namespaces by an implementation.
The namespace prefix xmlns
also has a special significance (it identifies a namespace declaration attribute), and it may not be redeclared. [err:XQ0070]
If the StringLiteral part of a namespace declaration is a zero-length string, any existing namespace binding for the given prefix is removed from the statically known namespaces. This feature provides a way to remove predeclared namespace prefixes such as local
.
When element or attribute names are compared, they are considered identical if the local parts and namespace URIs match on a codepoint basis. Namespace prefixes need not be identical for two names to match, as illustrated by the following example:
declare namespace xx = "http://example.org"; let $i := <foo:bar xmlns:foo = "http://example.org"> <foo:bing> Lentils </foo:bing> </foo:bar> return $i/xx:bing
Although the namespace prefixes xx
and foo
differ, both are bound to the namespace URI "http://example.org"
. Since xx:bing
and foo:bing
have the same local name and the same namespace URI, they match. The output of the above query is as follows.
<foo:bing xmlns:foo = "http://example.org"> Lentils </foo:bing>
[12] | DefaultNamespaceDecl |
::= | (("declare" "default" "element") | ("declare" "default" "function")) "namespace" StringLiteral |
Default namespace declarations can be used in a Prolog to facilitate the use of unprefixed QNames. The string literal used in a default namespace declaration must be a valid URI or a zero-length string. [err:XQ0046] The following kinds of default namespace declarations are supported:
A default element/type namespace declaration declares a namespace URI that is associated with unprefixed names of elements and types. This declaration is recorded as the default element/type namespace in the static context. A Prolog may contain at most one default element/type namespace declaration.[err:XQ0066] If the StringLiteral in a default element/type namespace declaration is a zero-length string, the default element/type namespace is set to "none," and unprefixed names of elements and types are considered to be in no namespace. The following example illustrates the declaration of a default namespace for elements and types:
declare default element namespace "http://example.org/names";
A default element/type namespace declaration may be overridden by a namespace declaration attribute in a direct element constructor.
A default function namespace declaration declares a namespace URI that is associated with unprefixed names of functions in function calls. This declaration is recorded as the default function namespace in the static context. A Prolog may contain at most one default function namespace declaration.[err:XQ0066] If the StringLiteral in a default function namespace declaration is a zero-length string, a static error is raised. [err:XQ0063] If no default function namespace is declared, the default function namespace is the namespace of XPath/XQuery functions, http://www.w3.org/2004/10/xpath-functions
(however, this default may be overridden by an implementation.) The following example illustrates the declaration of a default
function namespace:
declare default function namespace "http://example.org/math-functions";
The effect of declaring a default function namespace is that all functions in the default function namespace, including implicitly-declared constructor functions, are aliased with a name that has the original local name, but no namespace URI. The function may then be called using either its original name or its alias—that is, the namespace prefix becomes optional. When a function call uses a function name with no prefix, the local name of the function must match a function (including implicitly-declared constructor functions) in the default function namespace.[err:XP0017]
Note:
If a default namespace declaration sets the default function namespace to a zero-length string, then all function calls must use prefixed function names, because every function is in some namespace.
Unprefixed attribute names and variable names are in no namespace.
[21] | VarDecl |
::= | "declare" "variable" "$" VarName TypeDeclaration? ((":=" ExprSingle) | "external") |
[137] | VarName |
::= | QName |
[110] | TypeDeclaration |
::= | "as" SequenceType |
A variable declaration adds the static type of a variable to the in-scope variables, and may also add a value for the variable to the variable values. If the expanded QName of the variable is the same as that of another variable in in-scope variables, a static error is raised.[err:XQ0049]
If a variable declaration includes a type, that type is added to the static context as the type of the variable. If a variable declaration includes an expression but not an explicit type, the type of the variable inferred from static analysis of the expression and is added to the static context. If a variable declaration includes both a type and an expression, the value returned by the expression must match the declared type according to the rules for SequenceType matching; otherwise a type error is raised.[err:XP0004][err:XP0006]
[Definition: If a variable declaration includes an expression, the expression is called an initializing expression.] The initializing expression for a given variable must be evaluated before the evaluation of any expression that references the variable. The static context for an initializing expression includes all functions that are declared or imported anywhere in the Prolog, but it includes only those variables and namespaces that are declared or imported earlier in the Prolog than the variable that is being initialized. If an initializing expression cannot be evaluated because of a circularity (for example, it depends on a function that in turn depends on the value of the variable that is being initialized), a static error is raised.[err:XQ0054]
If the variable declaration includes the keyword external
, a value must be provided for the variable by the external environment before the query can be evaluated. If an external variable declaration also includes a declared type, the value provided by the external environment must match the declared type according to the rules for SequenceType matching (see 2.2.5 Consistency
Constraints). If an external variable declaration does not include a declared type, the type and a matching value must be provided by the external environment at evaluation time. The static type of such a variable is considered to be item()*
.
All variable names declared in a library module must (when expanded) be in the target namespace of the library module.[err:XQ0048] When a library module is imported, variables declared in the imported module are added to the in-scope variables of the importing module.
Variable names that have no namespace prefix are in no namespace. Variable declarations that have no namespace prefix may appear only in a main module.
The term variable declaration always refers to a declaration of a variable in a Prolog. The binding of a variable to a value in a query expression, such as a FLWOR expression, is known as a variable binding, and does not make the variable visible to an importing module.
Here are some examples of variable declarations:
The following declaration specifies both the type and the value of a variable. This declaration causes the type xs:integer
to be associated with variable $x
in the static context, and the value 7
to be associated with variable $x
in the dynamic context.
declare variable $x as xs:integer := 7;
The following declaration specifies a value but not a type. The static type of the variable is inferred from the static type of its value. In this case, the variable $x
has a static type of xs:decimal
, inferred from its value which is 7.5.
declare variable $x := 7.5;
The following declaration specifies a type but not a value. The keyword external
indicates that the value of the variable will be provided by the external environment. At evaluation time, if the variable $x
in the dynamic context does not have a value of type xs:integer
, a type error is raised.
declare variable $x as xs:integer external;
The following declaration specifies neither a type nor a value. It simply declares that the query depends on the existence of a variable named $x
, whose type and value will be provided by the external environment. During query analysis, the type of $x
is considered to be item()*
. During query evaluation, the dynamic context must include a type and a value for $x
, and its value must be compatible
with its type.
declare variable $x external;
In addition to the built-in functions described in [XQuery 1.0 and XPath 2.0 Functions and Operators], XQuery allows users to declare functions of their own. A function declaration specifies the name of the function, the names and datatypes of the parameters, and the datatype of the result. All datatypes are specified using the syntax described in 2.5 Types. A function declaration causes the declared function to be added to the function signatures of the module in which it appears.
[23] | FunctionDecl |
::= | "declare" "function" QName "(" ParamList? (")" | (")" "as" SequenceType)) (EnclosedExpr | "external") |
[24] | ParamList |
::= | Param ("," Param)* |
[25] | Param |
::= | "$" VarName TypeDeclaration? |
[110] | TypeDeclaration |
::= | "as" SequenceType |
A function declaration specifies whether a function is user-defined or external. [Definition: For a user-defined function, the function declaration includes an expression called the function body that defines how the result of the function is computed from its parameters.]. The static context for a function body includes all functions that are declared or imported anywhere in the Prolog, but it includes only those variables and namespaces that are declared or imported earlier in the Prolog than the function that is being defined.
[Definition: External functions are functions that are implemented outside the query environment.] For example, an XQuery implementation might provide a set of external functions in addition to the core function library described in [XQuery 1.0 and XPath 2.0 Functions and Operators]. External functions are identified by the keyword external
. The purpose of a
function declaration for an external function is to declare the datatypes of the function parameters and result, for use in type checking of the query that contains or imports the function declaration.
An XQuery implementation may provide a facility whereby external functions can be implemented using a host programming language, but it is not required to do so. If such a facility is provided, the protocols by which parameters are passed to an external function, and the result of the function is returned to the invoking query, are implementation-defined. An XQuery implementation may augment the type system of [XQuery 1.0 and XPath 2.0 Data Model] with additional types that are designed to facilitate exchange of data with host programming languages, or it may provide mechanisms for the user to define such types. For example, a type might be provided that encapsulates an object returned by an external function, such as an SQL database connection. These additional types, if defined, are considered to be derived by restriction from xdt:anyAtomicType
.
Every function must be in a namespace--that is, every declared function name must (when expanded) have a non-empty namespace URI. [err:XQ0060] Every function name declared in a library module must (when expanded) be in the target namespace of the library module.[err:XQ0048] It is a static error [err:XQ0045] if the function name in a function declaration (when expanded) is in any of the following namespaces:
http://www.w3.org/XML/1998/namespace
http://www.w3.org/2001/XMLSchema
http://www.w3.org/2001/XMLSchema-instance
http://www.w3.org/2004/10/xpath-functions
http://www.w3.org/2004/10/xpath-datatypes
If the expanded QName and arity (number of arguments) of the declared function are the same as the expanded QName and arity of another function in function signatures, a static error is raised.[err:XQ0034]
In order to allow main modules to declare functions for local use within the module without defining a new namespace, XQuery predefines the namespace prefix local
to the namespace http://www.w3.org/2004/10/xquery-local-functions
, and reserves this namespace for use in defining local functions.
If a function parameter is declared using a name but no type, its default type is item*
. If the result type is omitted from a function declaration, its default result type is item*
.
The parameters of a function declaration are considered to be variables whose scope is the function body. It is an static error [err:XQ0039] for a function declaration to have more than one parameter with the same name. The type of a function parameter can be any type that can be expressed as a SequenceType (see 2.5 Types).
The following example illustrates the declaration and use of a local function that accepts a sequence of employee
elements, summarizes them by department, and returns a sequence of dept
elements.
Using a function, prepare a summary of employees that are located in Denver.
declare function local:summary($emps as element(employee)*) as element(dept)* { for $d in fn:distinct-values($emps/deptno) let $e := $emps[deptno = $d] return <dept> <deptno>{$d}</deptno> <headcount> {fn:count($e)} </headcount> <payroll> {fn:sum($e/salary)} </payroll> </dept> }; local:summary(fn:doc("acme_corp.xml")//employee[location = "Denver"])
Rules for converting function arguments to their declared parameter types, and for converting the result of a function to its declared result type, are described in 3.1.5 Function Calls
A function declaration may be recursive—that is, it may reference itself. Mutually recursive functions, whose bodies reference each other, are also allowed. The following example declares a recursive function that computes the maximum depth of a node hierarchy, and calls the function to find the maximum depth of a particular document. In its declaration, the user-declared function local:depth
calls the built-in functions empty
and max
, which are in the
default function namespace.
Find the maximum depth of the document named partlist.xml
.
declare function local:depth($e as node()) as xs:integer { (: A node with no children has depth 1 :) (: Otherwise, add 1 to max depth of children :) if (fn:empty($e/*)) then 1 else fn:max(for $c in $e/* return local:depth($c)) + 1 }; local:depth(fn:doc("partlist.xml"))
Since a constructor function is effectively declared for every user-defined atomic type in the in-scope type definitions, a static error [err:XQ0034] is raised if the Prolog attempts to declare a function with the same expanded QName as any of these types.
The following grammar uses the same simple Extended Backus-Naur Form (EBNF) notation as [XML 1.0] with the following minor differences. The notation "< ... >" is used to indicate a grouping of terminals that together may help disambiguate the individual symbols. To help readability, this "< ... >" notation is absent in the EBNF in the main body of this document. This appendix is the normative version of the EBNF.
Comments on grammar productions are between '/*' and '*/' symbols - please note that these comments are normative. A 'gn:' prefix means a 'Grammar Note', and is meant as a clarification for parsing rules, and is explained in A.1.1 Grammar Notes. A 'ws:' prefix explains the whitespace rules for the production, the details of which are explained in A.2.2 Whitespace Rules
The following term definitions will be helpful in defining precisely this exposition.
[Definition: Each rule in the grammar defines one symbol, in the form]
symbol ::= expression
[Definition: A terminal is a single unit of the grammar that can not be further subdivided, and is specified in the EBNF by a character or characters in quotes, or a regular expression.] The following expressions are used to match strings of one or more characters in a terminal:
where N is a hexadecimal integer, the expression matches the character in [ISO/IEC 10646] whose canonical (UCS-4) code value, when interpreted as an unsigned binary number, has the value indicated. The number of leading zeros in the #xN form is insignificant; the number of leading zeros in the corresponding code value is governed by the character encoding in use and is not significant for XML.
matches any Char with a value in the range(s) indicated (inclusive).
matches any Char with a value among the characters enumerated. Enumerations and ranges can be mixed in one set of brackets.
matches any Char with a value outside the range indicated.
matches any Char with a value not among the characters given. Enumerations and ranges of forbidden values can be mixed in one set of brackets.
matches a literal string matching that given inside the double quotes.
matches a literal string matching that given inside the single quotes.
matches a production defined in the external specification as per the provided reference. For the purposes of this secification, the entire unit is defined as a terminal.
[Definition: A production combines symbols to form more complex patterns. ] The following productions serve as examples, where A and B represent simple expressions:
expression
is treated as a unit and may be combined as described in this list.
matches A
or nothing; optional A
.
matches A
followed by B
. This operator has higher precedence than alternation; thus A B | C D
is identical to (A B) | (C D)
.
matches A
or B
but not both.
matches any string that matches A
but does not match B
.
matches one or more occurrences of A
.Concatenation has higher precedence than alternation; thus A+ | B+
is identical to (A+) | (B+)
.
matches zero or more occurrences of A
. Concatenation has higher precedence than alternation; thus A* | B*
is identical to (A*) | (B*)
This section contains general notes on the EBNF productions, which may be helpful in understanding how to create a parser based on this EBNF, how to read the EBNF, and generally call out issues with the syntax. The notes below are referenced from the right side of the production, with the notation: /* gn: <id> */.
A look-ahead of one character is required to distinguish function patterns from a QName or keyword followed by a Pragma, MUExtension or Comment. For example: address (: this may be empty :)
may be mistaken for a call to a function named "address" unless this lookahead is employed. Another example is for (: whom the bell :) $tolls = 3 return $tolls
, where the keyword "for" must not be mistaken for a function name.
A tokenizer must be aware of the context in which the "<" pattern appears, in order to distinguish the "<" comparison operator from the "<" tag open symbol. The "<" comparison operator can not occur in the same places as a "<" tag open pattern.
The ValidateExpr in the exposition, which does not use the "< ... >" token grouping, presents the production in a much simplified, and understandable, form. The ValidateExpr presented in the appendix is technically correct, but structurally hard to understand, because of limitations of the "< ... >" token grouping.
The "/" presents an issue because it occurs either as a stand alone unit or as a leading prefix that expects a pattern to follow such as a QName or "*". Both of these patterns also may occur as patterns which are recognized in contexts where operators may occur. Thus, expressions such as "/ * 5" can easily be confused with the path expression "/*". Therefore, a stand-alone slash on the right hand side of an operator, will need to be parenthesized in order to stand alone, as in "(/) * 5". "5 * /", on the other hand, is legal syntax.
Expression comments are allowed inside expressions everywhere that ignorable whitespace is allowed. Note that expression comments are not allowed in constructor content.
Comments can nest within each other, as long as all "(:" and ":)" patterns are balanced, no matter where they occur within the outer comment.
Note:
Lexical analysis may typically handle nested comments by incrementing a counter for each "(:" pattern, and decrementing the counter for each ":)" pattern. The comment does not terminate until the counter is back to zero.
Following are some illustrative examples:
for (: set up loop :) $i in $x return $i
will parse correctly, ignoring the comment.
5 instance (: strange place for a comment :) of xs:integer
will also parse correctly, ignoring the comment.
<eg (: an example:)> $i//title </eg>
will cause a syntax error.
<eg> (: an example:) </eg>
will parse correctly, but characters inside the element is element content, and not an expression comment.
See Comments, Pragmas and Extensions for further information and examples.
An implementation's choice (see 2.6.5 XML and Names 1.1 Feature) to support the [XML 1.0] and [XML Names], or [XML 1.1] and [XML Names 1.1] lexical specification determines the external document from which to obtain the definition for this production. For convenience, XML 1.0 references are always used. In some cases, the XML 1.0 and XML 1.1 definitions may be exactly the same. Also
please note that these external productions follow the whitespace rules of their respective specifications, and not the rules of this specification, in particular A.2.2.1 Default Whitespace Handling. Thus prefix : localname
is not a valid QName for purposes of this specification, just as it is not permitted in a textual XML document. Also, comments are not permissible on either side of the colon.
Some unprefixed function names may be confused with expression syntax by the parser. For instance, if(foo)
could either be a function name invocation or an incomplete IfExpr. Therefore it is not legal syntax for a user to invoke functions with these names. See A.3 Reserved Function Names for a list of these names.
The '+' and '*' Kleene operators are tightly bound to the SequenceType expression, and have higher precedence than other uses of these symbols. Any occurrence of '+' and '*', as well as '?', following a sequence type is assumed to be an occurrence indicator. Thus, 4 treat as item() + - 5
is interpreted as (4 treat as item()+) - 5
, so that the '+' would be an occurrence operator, and the '-' in this case would be a subtraction operator. To
have this interpreted as an addition operator of a negative number, the form (4 treat as item()) + -5
would have to be used, so that the SequenceType expression is bounded by a parenthisis.
It is implementation-defined whether the lexical rules of [XML 1.0] and [XML Names]are followed, or alternatively, the lexical rules of [XML 1.1] and [XML Names 1.1] are followed.
Note:
Implementations that support the full [XML 1.1] character set may wish, for purposes of interoperability, to provide a mode that follows only the [XML 1.0] and [XML Names] lexical rules.
When patterns are simple string matches, the strings are embedded directly into the EBNF. In other cases, named terminals are used.
It is up to an implementation to decide on the exact tokenization strategy, which may be different depending on the parser construction. In the EBNF, the notation "< ... >" is used to indicate a grouping of terminals that together may help disambiguate the individual symbols.
When tokenizing, the longest possible match that is valid in the current context is preferred .
All keywords are case sensitive. Keywords are not reserved—that is, any QName may duplicate a keyword except as noted in A.3 Reserved Function Names.
Editorial note | |
The tables found in A.2.4 Lexical Rules of the previous draft have been made non-normative and removed from this document. They will be subsequently be re-published in a non-normative W3C Note. |
The entire set of terminals in XQuery 1.0 may be divided into two major classes, those that can act as token delimiters, and those that can not.
[Definition: A delimiting terminal may delimit adjacent non-delimiting terminals.] The following is the list of delimiting terminals:
, "<?", "?>", "::", "*", "$", "?", ")", "(", "{", ":", "/", "//", "=", "!=", "<=", "<<", ">=", ">>", ":=", "<", ">", "-", "+", "|", "@", "[", "]", ",", ";", "%%%", """, ".", "..", "<![CDATA[", "]]>", PredefinedEntityRef, CharRef, "/>", "</", "{{", "}}", EscapeQuot, EscapeApos, "'", Pragma, "(::", "::)", Comment, "(:", ":)", "<!--", "-->", S, "}"
[Definition: Non-delimiting terminals generally start and end with alphabetic characters or digits. Adjacent non-delimiting terminals must be delimited by a delimiting terminal.] The following is the list of non-delimiting terminals:
DecimalLiteral, DoubleLiteral, StringLiteral, "xquery", "version", "encoding", "at", "module", "namespace", "child", "descendant", "parent", "attribute", "self", "descendant-or-self", "ancestor", "following-sibling", "preceding-sibling", "following", "preceding", "ancestor-or-self", "declare", "function", "ordering", "ordered", "unordered", "default", "order", "inherit-namespaces", "yes", "no", "external", "or", "and", "div", "idiv", "mod", "in", ValidationMode, "construction", "satisfies", "return", "then", "else", "xmlspace", "base-uri", "preserve", "strip", "to", "where", "collation", "intersect", "union", "except", "as", "case", "instance", "of", "castable", "item", "element", "schema-element", "schema-attribute", "processing-instruction", "comment", "text", "empty", "import", "schema", "is", "eq", "ne", "gt", "ge", "lt", "le", "some", "every", "for", "let", "cast", "treat", "validate", Digits, "document-node", "document", "node", "if", "typeswitch", "by", "stable", "ascending", "descending", "greatest", "least", "variable", ExtensionContents, CommentContents, "pragma", "extension", QName, NCName
[Definition: Whitespace characters are defined by [http://www.w3.org/TR/REC-xml#NT-S] when these characters occur outside of a StringLiteral.]
[Definition: Unless otherwise specified (see A.2.2.2 Explicit Whitespace Handling), Ignorable whitespace may occur between terminals, and is not significant to the parse tree. For readability, whitespace may be used in most expressions even though not explicitly notated in the EBNF. All allowable whitespace that is not explicitly specified in the EBNF is ignorable whitespace, and converse, this term does not apply to whitespace that is explicitly specified. ] Whitespace is allowed before the first token and after the last token of an expressiona module. Whitespace is optional between delimiting terminals. Whitespace is required to prevent two adjacent non-delimiting terminal from being (mis-)recognized as one. Comments, Pragmas, and MUExtensions may also act as "whitespace" to prevent two adjacent tokens from being recognized as one.. Some illustrative examples are as follows:
foo- foo
is a syntax error. "foo-" would be recognized as a QName.
foo -foo
parses the same as foo - foo
, two QNames separated by a subtraction operator. The parser would match the first "foo" as a QName. The parser would then expect a to match an operator, which is satisfied by "-" (but not "-foo"). The last foo would then be matched as another QName.
foo(: This is a comment :)- foo
also parses the same as foo - foo
. This is because the comment prevents the two adjacent tokens from being recognized as one.
foo-foo
parses as a single QName. This is because "-" is a valid character in a QName. When used as an operator after the characters of a name, the "-" must be separated from the name, e.g. by using whitespace or parentheses.
10div 3
results in a syntax error, since the "10" and the "div" would both be non-delimiting terminals and must be separated by delimiting terminals in order to be recognized.
10 div3
also results in a syntax error, since the "div" and the "3" would both be non-delimiting terminals and must be separated by delimiting terminals in order to be recognized.
10div3
also results in a syntax error, since the "10", "div" and the "3" would all be non-delimiting terminals and must be separated by delimiting terminals in order to be recognized.
Explict whitespace notation is specified with the EBNF productions, when it is different from the default rules, as follows. These notations do not inherit. In other words, if EBNF rule is marked as /* ws: explicit */, the rule does not automatically apply to all the 'child' EBNF productions of that rule.
"ws: explicit" means that the EBNF notation S
explicitly notates where whitespace is allowed. In productions with this notation, A.2.2.1 Default Whitespace Handling does not apply. Comments, Pragmas, and MUExtensions are also not allowed in these productions.
Whitespace is not freely allowed in the direct Constructor productions, but is specified explicitly in the grammar, in order to be more consistent with XML.
Pragmas and MUExtensions may be used anywhere that ignorable whitespace is allowed. Within a Pragma or MUExtension, the extension content may consist of any sequence of characters that does not include the sequence "::)". Pragmas, and MUExtensions are not allowed to nest. Comments are allowed to nest, though the content of a comment must have balanced comment delimiters without regard to structure. Some illustrative examples:
(: is this a comment? ::)
is a legal Comment.
(: can I comment out a (:: pragma foo ::) like this? :)
is a legal Comment. The inner pragma is seen as a nested comment in this case.
(: is this a comment? ::) or an error? :)
must produce a syntax error. Any unbalanced nesting of "(:" and ":)" will result in an error.
(: what about a partial (:: pragma? :)
must produce a syntax error. Any unbalanced nesting of "(:" and ":)" will result in an error.
(:: pragma foo with a comment (: is this ok? :) or not ::)
is a legal Pragma. The inner "comment" is seen as part of the extension content in this case.
(:: pragma foo with a comment (: is this a comment? ::) or an error? :) ::)
is a syntax error. "::)" patterns are not allowed inside pragma's and extensions.
(:: pragma foo with a comment (: what about a partial (:: pragma? :) ::)
is a legal Pragma. The inner "comment" and "(::" are seen as part of the extension content in this case.
(: commenting out a (: comment :) may be confusing, but often helpful :)
is a legal Comment, since balanced nesting of comments is allowed.
"this is just a string :)"
is a legal expression. However, (: "this is just a string :)" :)
will cause a syntax error. Likewise, "this is another string (:"
is a legal expression, but (: "this is another string (:" :)
will cause a syntax error. It is a limitation of nested comments that literal content can cause unbalanced nesting of comments.
The following is a list of names that must not be used as user function names in an unprefixed form, because these functions could be confused with expression syntax. Users should not have unprefixed invocations of functions with these names, and if they want to protect themselves from future changes they should use the prefixed form, or put a distinctive string in their function names.
attribute
comment
document-node
element
empty
if
item
node
processing-instruction
text
type
typeswitch
The grammar defines built-in precedence, which is summarised here. Operators that have a lower precedence number can not be contained by operators with a higher precedence number. Operators may contain other operators with the same precedence number on the right-hand-side. In the cases where a number of operators are at the same precedence level, the operators are applied from left to right.
The operators in order of increasing precedence are:
1 | (comma) |
2 | for, some, every, typeswitch, if |
3 | or |
4 | and |
5 | eq, ne, lt, le, gt, ge, =, !=, <, <=, >, >=, is, <<, >> |
6 | to |
7 | +, - |
8 | *, div, idiv, mod |
9 | union, | |
10 | intersect, except |
11 | instance of |
12 | treat |
13 | castable |
14 | cast |
15 | -(unary), +(unary) |
16 | ?, *(OccurrenceIndicator), +(OccurrenceIndicator) |
16 | validate, /, // |
17 | [ ], ( ) |
[Definition: Under certain circumstances, an atomic value can be promoted from one type to another. Numeric type promotion is used in function calls (see 3.1.5 Function Calls) and in processing of operators that accept numeric operands (see B.2 Operator Mapping).] The following numeric type promotions are permitted:
A value of type xs:float
(or any type derived by restriction from xs:float
) can be promoted to the type xs:double
. The result is the xs:double
value that is the same as the original value.
A value of type xs:decimal
(or any type derived by restriction from xs:decimal
, including xs:integer
) can be promoted to either of the types xs:float
or xs:double
. The result of this promotion is created by casting the original value to the required type. This kind of promotion may cause loss of precision.
Note that numeric type promotion is different from subtype substitution. For example:
A function that expects a parameter $p
of type xs:float
can be invoked with a value of type xs:decimal
. This is an example of numeric type promotion. The value is actually converted to the expected type. Within the body of the function, $p instance of xs:decimal
returns false
.
A function that expects a parameter $p
of type xs:decimal
can be invoked with a value of type xs:integer
. This is an example of subtype substitution. The value retains its original type. Within the body of the function, $p instance of xs:integer
returns true
.
The operator mapping tables in this section list the combinations of types for which the various operators of XQuery are defined. [Definition: For each operator and valid combination of operand types, the operator mapping tables specify a result type and an operator function that implements the semantics of the operator for the given types.] The definitions of the operator functions are given in [XQuery 1.0 and XPath 2.0 Functions and Operators]. The result of an operator may be the raising of an error by its operator function, as defined in [XQuery 1.0 and XPath 2.0 Functions and Operators]. In some cases, the operator function does not implement the full semantics of a given operator. For the definition of each operator (including its behavior for empty sequences or sequences of length greater than one), see the descriptive material in the main part of this document.
The and
and or
operators are defined directly in the main body of this document, and do not occur in the operator mapping tables.
Any operator listed in the operator mapping tables may be validly applied to an operand of type AT if the table calls for an operand of type ET and type-matches(
ET, AT)
is true
(see 2.5.4 SequenceType Matching). For example, a table entry indicates that the gt
operator may be applied to two xs:date
operands, returning xs:boolean
. Therefore, the
gt
operator may also be applied to two (possibly different) subtypes of xs:date
, also returning xs:boolean
.
[Definition: When referring to a type, the term numeric denotes the types xs:integer
, xs:decimal
, xs:float
, and xs:double
.] An operator whose operands and result are designated as numeric might be thought of as representing four operators, one for each of the numeric types. For example, the numeric +
operator might be thought of as
representing the following four operators:
Operator | First operand type | Second operand type | Result type |
+ |
xs:integer |
xs:integer |
xs:integer |
+ |
xs:decimal |
xs:decimal |
xs:decimal |
+ |
xs:float |
xs:float |
xs:float |
+ |
xs:double |
xs:double |
xs:double |
A numeric operator may be validly applied to an operand of type AT if type-matches(
ET, AT)
is true where ET is any of the four numeric types. If the result type of an operator is listed as numeric, it means "the first type in the ordered list (xs:integer, xs:decimal, xs:float, xs:double)
into which all operands can be converted by subtype substitution and numeric type promotion." As an example, suppose that the type hatsize
is derived from xs:integer
and the type shoesize
is derived from xs:float
. Then if the +
operator is invoked with operands of type hatsize
and shoesize
, it returns a result of type xs:float
. Similarly, if +
is invoked with two operands of type hatsize
it
returns a result of type xs:integer
.
[Definition: In the operator mapping tables, the term Gregorian refers to the types xs:gYearMonth
, xs:gYear
, xs:gMonthDay
, xs:gDay
, and xs:gMonth
.] For binary operators that accept two Gregorian-type operands, both operands must have the same type (for example, if one operand is of type xs:gDay
, the other operand must be of type xs:gDay
.)
Operator | Type(A) | Type(B) | Function | Result type |
---|---|---|---|---|
A + B | numeric | numeric | op:numeric-add(A, B) | numeric |
A + B | xs:date | xdt:yearMonthDuration | op:add-yearMonthDuration-to-date(A, B) | xs:date |
A + B | xdt:yearMonthDuration | xs:date | op:add-yearMonthDuration-to-date(B, A) | xs:date |
A + B | xs:date | xdt:dayTimeDuration | op:add-dayTimeDuration-to-date(A, B) | xs:date |
A + B | xdt:dayTimeDuration | xs:date | op:add-dayTimeDuration-to-date(B, A) | xs:date |
A + B | xs:time | xdt:dayTimeDuration | op:add-dayTimeDuration-to-time(A, B) | xs:time |
A + B | xdt:dayTimeDuration | xs:time | op:add-dayTimeDuration-to-time(B, A) | xs:time |
A + B | xs:dateTime | xdt:yearMonthDuration | op:add-yearMonthDuration-to-dateTime(A, B) | xs:dateTime |
A + B | xdt:yearMonthDuration | xs:dateTime | op:add-yearMonthDuration-to-dateTime(B, A) | xs:dateTime |
A + B | xs:dateTime | xdt:dayTimeDuration | op:add-dayTimeDuration-to-dateTime(A, B) | xs:dateTime |
A + B | xdt:dayTimeDuration | xs:dateTime | op:add-dayTimeDuration-to-dateTime(B, A) | xs:dateTime |
A + B | xdt:yearMonthDuration | xdt:yearMonthDuration | op:add-yearMonthDurations(A, B) | xdt:yearMonthDuration |
A + B | xdt:dayTimeDuration | xdt:dayTimeDuration | op:add-dayTimeDurations(A, B) | xdt:dayTimeDuration |
A - B | numeric | numeric | op:numeric-subtract(A, B) | numeric |
A - B | xs:date | xs:date | fn:subtract-dates-yielding-dayTimeDuration(A, B) | xdt:dayTimeDuration |
A - B | xs:date | xdt:yearMonthDuration | op:subtract-yearMonthDuration-from-date(A, B) | xs:date |
A - B | xs:date | xdt:dayTimeDuration | op:subtract-dayTimeDuration-from-date(A, B) | xs:date |
A - B | xs:time | xs:time | op:subtract-times(A, B) | xdt:dayTimeDuration |
A - B | xs:time | xdt:dayTimeDuration | op:subtract-dayTimeDuration-from-time(A, B) | xs:time |
A - B | xs:dateTime | xs:dateTime | fn:subtract-dateTimes-yielding-dayTimeDuration(A, B) | xdt:dayTimeDuration |
A - B | xs:dateTime | xdt:yearMonthDuration | op:subtract-yearMonthDuration-from-dateTime(A, B) | xs:dateTime |
A - B | xs:dateTime | xdt:dayTimeDuration | op:subtract-dayTimeDuration-from-dateTime(A, B) | xs:dateTime |
A - B | xdt:yearMonthDuration | xdt:yearMonthDuration | op:subtract-yearMonthDurations(A, B) | xdt:yearMonthDuration |
A - B | xdt:dayTimeDuration | xdt:dayTimeDuration | op:subtract-dayTimeDurations(A, B) | xdt:dayTimeDuration |
A * B | numeric | numeric | op:numeric-multiply(A, B) | numeric |
A * B | xdt:yearMonthDuration | numeric | op:multiply-yearMonthDuration(A, B) | xdt:yearMonthDuration |
A * B | numeric | xdt:yearMonthDuration | op:multiply-yearMonthDuration(B, A) | xdt:yearMonthDuration |
A * B | xdt:dayTimeDuration | numeric | op:multiply-dayTimeDuration(A, B) | xdt:dayTimeDuration |
A * B | numeric | xdt:dayTimeDuration | op:multiply-dayTimeDuration(B, A) | xdt:dayTimeDuration |
A idiv B | numeric | numeric | op:numeric-integer-divide(A, B) | xs:integer |
A div B | numeric | numeric | op:numeric-divide(A, B) | numeric; but xs:decimal if both operands are xs:integer |
A div B | xdt:yearMonthDuration | numeric | op:divide-yearMonthDuration(A, B) | xdt:yearMonthDuration |
A div B | xdt:dayTimeDuration | numeric | op:divide-dayTimeDuration(A, B) | xdt:dayTimeDuration |
A div B | xdt:yearMonthDuration | xdt:yearMonthDuration | op:divide-yearMonthDuration-by-yearMonthDuration (A, B) | xs:decimal |
A div B | xdt:dayTimeDuration | xdt:dayTimeDuration | op:divide-dayTimeDuration-by-dayTimeDuration (A, B) | xs:decimal |
A mod B | numeric | numeric | op:numeric-mod(A, B) | numeric |
A eq B | numeric | numeric | op:numeric-equal(A, B) | xs:boolean |
A eq B | xs:boolean | xs:boolean | op:boolean-equal(A, B) | xs:boolean |
A eq B | xs:string | xs:string | op:numeric-equal(fn:compare(A, B), 1) | xs:boolean |
A eq B | xs:date | xs:date | op:date-equal(A, B) | xs:boolean |
A eq B | xs:time | xs:time | op:time-equal(A, B) | xs:boolean |
A eq B | xs:dateTime | xs:dateTime | op:datetime-equal(A, B) | xs:boolean |
A eq B | xdt:yearMonthDuration | xdt:yearMonthDuration | op:yearMonthDuration-equal(A, B) | xs:boolean |
A eq B | xdt:dayTimeDuration | xdt:dayTimeDuration | op:dayTimeDuration-equal(A, B) | xs:boolean |
A eq B | Gregorian | Gregorian | op:gYear-equal(A, B) etc. | xs:boolean |
A eq B | xs:hexBinary | xs:hexBinary | op:hex-binary-equal(A, B) | xs:boolean |
A eq B | xs:base64Binary | xs:base64Binary | op:base64-binary-equal(A, B) | xs:boolean |
A eq B | xs:anyURI | xs:anyURI | op:anyURI-equal(A, B) | xs:boolean |
A eq B | xs:QName | xs:QName | op:QName-equal(A, B) | xs:boolean |
A eq B | xs:NOTATION | xs:NOTATION | op:NOTATION-equal(A, B) | xs:boolean |
A ne B | numeric | numeric | fn:not(op:numeric-equal(A, B)) | xs:boolean |
A ne B | xs:boolean | xs:boolean | fn:not(op:boolean-equal(A, B)) | xs:boolean |
A ne B | xs:string | xs:string | fn:not(op:numeric-equal(fn:compare(A, B), 1)) | xs:boolean |
A ne B | xs:date | xs:date | fn:not(op:date-equal(A, B)) | xs:boolean |
A ne B | xs:time | xs:time | fn:not(op:time-equal(A, B)) | xs:boolean |
A ne B | xs:dateTime | xs:dateTime | fn:not(op:datetime-equal(A, B)) | xs:boolean |
A ne B | xdt:yearMonthDuration | xdt:yearMonthDuration | fn:not(op:yearMonthDuration-equal(A, B)) | xs:boolean |
A ne B | xdt:dayTimeDuration | xdt:dayTimeDuration | fn:not(op:dayTimeDuration-equal(A, B) | xs:boolean |
A ne B | Gregorian | Gregorian | fn:not(op:gYear-equal(A, B)) etc. | xs:boolean |
A ne B | xs:hexBinary | xs:hexBinary | fn:not(op:hex-binary-equal(A, B)) | xs:boolean |
A ne B | xs:base64Binary | xs:base64Binary | fn:not(op:base64-binary-equal(A, B)) | xs:boolean |
A ne B | xs:anyURI | xs:anyURI | fn:not(op:anyURI-equal(A, B)) | xs:boolean |
A ne B | xs:QName | xs:QName | fn:not(op:QName-equal(A, B)) | xs:boolean |
A ne B | xs:NOTATION | xs:NOTATION | fn:not(op:NOTATION-equal(A, B)) | xs:boolean |
A gt B | numeric | numeric | op:numeric-greater-than(A, B) | xs:boolean |
A gt B | xs:boolean | xs:boolean | op:boolean-greater-than(A, B) | xs:boolean |
A gt B | xs:string | xs:string | op:numeric-greater-than(fn:compare(A, B), 0) | xs:boolean |
A gt B | xs:date | xs:date | op:date-greater-than(A, B) | xs:boolean |
A gt B | xs:time | xs:time | op:time-greater-than(A, B) | xs:boolean |
A gt B | xs:dateTime | xs:dateTime | op:datetime-greater-than(A, B) | xs:boolean |
A gt B | xdt:yearMonthDuration | xdt:yearMonthDuration | op:yearMonthDuration-greater-than(A, B) | xs:boolean |
A gt B | xdt:dayTimeDuration | xdt:dayTimeDuration | op:dayTimeDuration-greater-than(A, B) | xs:boolean |
A lt B | numeric | numeric | op:numeric-less-than(A, B) | xs:boolean |
A lt B | xs:boolean | xs:boolean | op:boolean-less-than(A, B) | xs:boolean |
A lt B | xs:string | xs:string | op:numeric-less-than(fn:compare(A, B), 0) | xs:boolean |
A lt B | xs:date | xs:date | op:date-less-than(A, B) | xs:boolean |
A lt B | xs:time | xs:time | op:time-less-than(A, B) | xs:boolean |
A lt B | xs:dateTime | xs:dateTime | op:datetime-less-than(A, B) | xs:boolean |
A lt B | xdt:yearMonthDuration | xdt:yearMonthDuration | op:yearMonthDuration-less-than(A, B) | xs:boolean |
A lt B | xdt:dayTimeDuration | xdt:dayTimeDuration | op:dayTimeDuration-less-than(A, B) | xs:boolean |
A ge B | numeric | numeric | op:numeric-greater-than(A, B) or op:numeric-equal(A, B) | xs:boolean |
A ge B | xs:boolean | xs:boolean | fn:not(op:boolean-less-than(A, B)) | xs:boolean |
A ge B | xs:string | xs:string | op:numeric-greater-than(fn:compare(A, B), -1) | xs:boolean |
A ge B | xs:date | xs:date | fn:not(op:date-less-than(A, B)) | xs:boolean |
A ge B | xs:time | xs:time | fn:not(op:time-less-than(A, B)) | xs:boolean |
A ge B | xs:dateTime | xs:dateTime | fn:not(op:datetime-less-than(A, B)) | xs:boolean |
A ge B | xdt:yearMonthDuration | xdt:yearMonthDuration | fn:not(op:yearMonthDuration-less-than(A, B)) | xs:boolean |
A ge B | xdt:dayTimeDuration | xdt:dayTimeDuration | fn:not(op:dayTimeDuration-less-than(A, B)) | xs:boolean |
A le B | numeric | numeric | op:numeric-less-than(A, B) or op:numeric-equal(A, B) | xs:boolean |
A le B | xs:boolean | xs:boolean | fn:not(op:boolean-greater-than(A, B)) | xs:boolean |
A le B | xs:string | xs:string | op:numeric-less-than(fn:compare(A, B), 1) | xs:boolean |
A le B | xs:date | xs:date | fn:not(op:date-greater-than(A, B)) | xs:boolean |
A le B | xs:time | xs:time | fn:not(op:time-greater-than(A, B)) | xs:boolean |
A le B | xs:dateTime | xs:dateTime | fn:not(op:datetime-greater-than(A, B)) | xs:boolean |
A le B | xdt:yearMonthDuration | xdt:yearMonthDuration | fn:not(op:yearMonthDuration-greater-than(A, B)) | xs:boolean |
A le B | xdt:dayTimeDuration | xdt:dayTimeDuration | fn:not(op:dayTimeDuration-greater-than(A, B)) | xs:boolean |
A is B | node() | node() | op:is-same-node(A, B) | xs:boolean |
A << B | node() | node() | op:node-before(A, B) | xs:boolean |
A >> B | node() | node() | op:node-after(A, B) | xs:boolean |
A union B | node()* | node()* | op:union(A, B) | node()* |
A | B | node()* | node()* | op:union(A, B) | node()* |
A intersect B | node()* | node()* | op:intersect(A, B) | node()* |
A except B | node()* | node()* | op:except(A, B) | node()* |
A to B | xs:integer | xs:integer | op:to(A, B) | xs:integer* |
A , B | item()* | item()* | op:concatenate(A, B) | item()* |
Operator | Operand type | Function | Result type |
---|---|---|---|
+ A | numeric | op:numeric-unary-plus(A) | numeric |
- A | numeric | op:numeric-unary-minus(A) | numeric |
The tables in this section describe how values are assigned to the various components of the static context and dynamic context, and to the parameters that control the serialization process.
The following table describes the components of the static context. The following aspects of each component are described:
Default value: This is the value of the component if it is not overridden or augmented by the implementation or by a query.
Can be overwritten or augmented by implementation: Indicates whether an XQuery implementation is allowed to replace the default value of the component by a different value and/or to augment the default value by additional values.
Can be overwritten or augmented by a query: Indicates whether a query is allowed to replace and/or augment the initial value provided by default or by the implementation. If so, indicates how this is accomplished (for example, by a declaration in the prolog).
Scope: Indicates where the component is applicable. "Global" indicates that the component applies globally, throughout all the modules used in a query. "Module" indicates that the component applies throughout a module. "Lexical" indicates that the component applies within the expression in which it is defined (equivalent to "module" if the component is declared in a Prolog.)
Consistency Rules: Indicates rules that must be observed in assigning values to the component. Additional consistency rules may be found in 2.2.5 Consistency Constraints.
Component | Default predefined value | Can be overwritten or augmented by implementation? | Can be overwritten or augmented by a query? | Scope | Consistency rules |
---|---|---|---|---|---|
XPath 1.0 Compatibility Mode | false |
no | no | global | Must be false . |
Statically known namespaces | fn , xml , xs , xsi , xdt , local |
overwriteable and augmentable (except for xml ) |
overwriteable and augmentable by prolog or element constructor | lexical | Only one namespace can be assigned to a given prefix per lexical scope. |
Default element/type namespace | no namespace | overwriteable | overwriteable by prolog or element constructor | lexical | Only one default namespace per lexical scope. |
Default function namespace | fn |
overwriteable (not recommended) | overwriteable by prolog | module | None. |
In-scope type definitions | Built-in types in xs , xdt |
augmentable | augmentable by schema import in prolog | module | Only one definition per global or local type. |
In-scope element declarations | none | augmentable | augmentable by schema import in prolog | module | Only one definition per global or local element name. |
In-scope attribute declarations | none | augmentable | augmentable by schema import in prolog | module | Only one definition per global or local attribute name. |
In-scope variables | none | augmentable | overwriteable and augmentable by prolog and by variable-binding expressions | lexical | Only one definition per variable per lexical scope. |
Context item static type | none (raises error on access) |
augmentable | not explicitly, but can be influenced by expressions | lexical | None. |
Function signatures | Functions in fn namespace, and constructors for built-in atomic types |
augmentable | augmentable by module import and by function declaration in prolog | module | Each function must have a unique expanded QName and number of arguments. |
Statically known collations | only the default collation | augmentable | no | module | Each URI uniquely identifies a collation. |
Default collation | Unicode codepoint collation | overwriteable | overwriteable by prolog | module | None. |
Construction mode | preserve |
overwriteable | overwriteable by prolog | module | Value must be preserve or strip . |
Ordering mode | ordered |
overwriteable | overwriteable by prolog or expression | lexical | Value must be ordered or unordered . |
Default ordering for empty sequences | implementation-defined | overwriteable | overwriteable by prolog | module | Value must be greatest or least . |
XMLSpace policy | strip |
overwriteable | overwriteable by prolog | module | Value must be preserve or strip . |
Namespace inheritance mode | yes |
overwriteable | overwriteable by prolog | module | Value must be yes or no . |
Base URI | none | overwriteable | overwriteable by prolog | module | Value must be a valid lexical representation of the type xs:anyURI. |
Statically known documents | none | augmentable | no | module | None. |
Statically known collections | none | augmentable | no | module | None. |
Statically known default collection type | node()* |
overwriteable | no | module | None. |
XQuery Flagger status | off |
overwriteable | no | global | Value must be on or off . |
XQuery Static Flagger status | off |
overwriteable | no | global | Value must be on or off . |
The following table describes the components of the dynamic context. The following aspects of each component are described:
Default value: This is the value of the component if it is not overridden or augmented by the implementation or by a query.
Can be overwritten or augmented by implementation: Indicates whether an XQuery implementation is allowed to replace the default value of the component by a different value and/or to augment the default value by additional values.
Can be overwritten or augmented by a query: Indicates whether a query is allowed to replace and/or augment the initial value provided by default or by the implementation. If so, indicates how this is accomplished.
Scope: Indicates where the component is applicable. "Global" indicates that the component applies globally, throughout all the modules used in a query, and remains constant during evaluation of a query. "Dynamic" indicates that evalation of an expression may influence the value of the component for that expression and for nested expressions.
Consistency Rules: Indicates rules that must be observed in assigning values to the component. Additional consistency rules may be found in 2.2.5 Consistency Constraints.
Component | Default predefined value | Can be overwritten or augmented by implementation? | Can be overwritten or augmented by a query? | Scope | Consistency rules |
---|---|---|---|---|---|
Context item | none | overwriteable | overwritten during evaluation of path expressions and predicates | dynamic | none |
Context position | none | overwriteable | overwritten during evaluation of path expressions and predicates | dynamic | Must be consistent with context item and context size |
Context size | none | overwriteable | overwritten during evaluation of path expressions and predicates | dynamic | Must be consistent with context item |
Variable values | none | augmentable | overwriteable and augmentable by prolog and by variable-binding expressions | dynamic | Names and values must be consistent with in-scope variables. |
Function implementations | Functions in fn namespace, and constructors for built-in atomic types | augmentable | augmentable by module import and by function declaration in prolog | global | Must be consistent with function signatures |
Current dateTime | none | Must be initialized by implementation | no | global | Must include a timezone. Remains constant during evaluation of a query. |
Implicit timezone | none | Must be initialized by implementation | no | global | Remains constant during evaluation of a query. |
Available documents | none | Must be initialized by implementation | no | global | None |
Available collections | none | Must be initialized by implementation | no | global | None |
Default collection | none | Must be initialized by implementation | no | global | None |
The following table specifies default values for the parameters that control the process of serializing a Data Model instance into XML notation (method = "xml"
). The meanings of the various parameters are defined in [XSLT 2.0 and XQuery 1.0 Serialization]. For each parameter, an XQuery implementation may (but is not required to) provide a means whereby a user can override the default value.
Parameter | Default Value |
---|---|
encoding | implementation-defined choice between "utf-8" and "utf-16" |
cdata-section-elements | empty |
doctype-system | (none) |
doctype-public | (none) |
escape-uri-attributes | no |
indent | no |
media-type | implementation-defined |
normalization-form | implementation-defined |
omit-xml-declaration | yes |
standalone | none |
use-character-maps | empty |
version | 1.0 |
byte-order-mark | implementation-defined |
Editorial note | |
As of the date of this publication, XQueryX has not incorporated recent language changes; it will be made consistent with this document in its next edition. |
It is a static error if analysis of an expression relies on some component of the static context that has not been assigned a value.
It is a dynamic error if evaluation of an expression relies on some part of the dynamic context that has not been assigned a value.
It is a static error if an expression is not a valid instance of the grammar defined in A.1 EBNF.
During the analysis phase, it is a type error if the static typing feature is in effect and an expression is found to have a static type that is not appropriate for the context in which the expression occurs.
During the analysis phase, it is a static error if the static typing feature is in effect and the static type assigned to an expression other than the expression ()
or data(())
is the empty type.
During the evaluation phase, it is a type error if a value does not match a required type as specified by the matching rules in 2.5.4 SequenceType Matching.
It is a type error if the fn:data
function is applied to a node whose type annotation denotes a complex type with non-mixed complex content.
It is a static error if an expression refers to an element name, attribute name, type name, function name, namespace prefix, or variable name that is not defined in the static context, except within an ElementTest or an AttributeTest.
An implementation that does not support the Schema Import Feature may raise a static error if a Prolog contains a schema import.
An implementation that does not support the Full Axis Feature must raise a static error if it encounters a reference to an optional axis that it does not support.
If the Schema Import Feature is in effect, it is a static error if the set of definitions contained in all imported schemas do not satisfy the conditions for schema validity specified in Sections 3 and 5 of [XML Schema] Part 1. In particular, the definitions must be valid, they must be complete, and they must be unique -- that is, the pool of definitions must not contain two or more schema components with the same name and target namespace.
It is a static error if an implementation supports a pragma but determines that its content is invalid.
It is a static error if an implementation does not support a must-understand extension or an implementation does support a must-understand extension and the implementation determines that the character content is invalid.
It is a static error if the XQuery Flagger is enabled and the query contains a must-understand extension.
An implementation that does not support the Module Feature raises a static error if it encounters a module declaration or a module import.
It is a static error if the expanded QName and number of arguments in a function call do not match the name and arity of a function signature in the static context.
It is a type error if the result of the last step in a path expression contains both nodes and atomic values.
It is a type error if the result of an step (other than the last step) in a path expression contains an atomic value.
It is a type error if in an axis expression, the context item is not a node.
It is a dynamic error if the argument of a cast expression or constructor function cannot be cast to the required type.
It is a static error if the value of a namespace declaration attribute is not a literal string.
(Not currently used.)
It is a type error if the content sequence in an element constructor contains an attribute node following a node that is not an attribute node.
It is a dynamic error if any attribute of a constructed element does not have a name that is distinct from the names of all other attributes of the constructed element.
It is a dynamic error if the result of the content expression of a computed processing instruction constructor contains the string "?>
".
In a validate expression, it is a dynamic error if validation fails.
(Not currently used.)
It is a dynamic error in a cast expression if the input value does not satisfy the facets of the target type.
It is a type error if the argument of a validate
expression does not evaluate to exactly one document or element node.
It is a static error if the version number specified in a version declaration is not supported by the implementation.
A static error is raised if a Prolog contains more than one base URI declaration.
It is a static error if a Prolog contains multiple declarations for the same namespace prefix.
It is a static error if multiple functions declared or imported by a module have the same expanded QName and the same number of arguments.
It is a static error to import two schema components that both define the same name in the same symbol space and in the same scope.
It is a type error to import a module if the importing module's in-scope type definitions do not include definitions for the type names that appear in variable declarations, function parameters, or function returns found in the imported module.
(Not currently used.)
It is a static error if a Prolog contains more than one default collation declaration, or the value specified by a default collation declaration does not identify a collation known to the implementation.
It is a static error for a function declaration to have more than one parameter with the same name.
It is a static error if the attributes specified by a direct element constructor do not have distinct names.
It is a dynamic error if the value of the name expression in a computed processing instruction constructor cannot be cast to the type xs:NCName
.
(Not currently used.)
(Not currently used.)
It is a dynamic error if the name expression of a computed attribute constructor returns a QName that is in the namespace http://www.w3.org/TR/REC-xml-names
(corresponding to namespace prefix xmlns
), or returns a QName that is in no namespace and has local name xmlns
.
It is a static error if the function name in a function declaration is in one of the following namespaces: http://www.w3.org/XML/1998/namespace, http://www.w3.org/2001/XMLSchema, http://www.w3.org/2001/XMLSchema-instance, http://www.w3.org/2004/10/xpath-functions, http://www.w3.org/2004/10/xpath-datatypes
.
It is a static error if a string that is required to contain a valid URI does not contain a valid lexical form according to the definition of xs:anyURI
in [XML Schema].
It is a static error if multiple module imports in the same Prolog specify the same target namespace.
It is a static error if a function or variable declared in a library module is not in the target namespace of the library module.
It is a static error if more than one variable declared or imported by a module has the same expanded QName.
It is a dynamic error if the dynamic type of the operand of a treat
expression does not match the type specified by the treat
expression.
It is a static error if a QName that is used as an AtomicType in a SequenceType is not defined in the in-scope type definitions as an atomic type.
(Not currently used.)
(Not currently used.)
It is a static error if the initializing expression in a variable declaration cannot be executed because of a circularity (for example, the expression depends on a function that in turn depends on the value of the initialized variable).
It is a static error if a Prolog contains more than one inherit-namespaces declaration.
It is a static error if the target namespace specified in a module import is the same as the target namespace of the importing module.
It is a static error if a schema import binds a namespace prefix but does not specify a target namespace other than a zero-length string.
It is a static error if multiple schema imports specify the same target namespace.
It is a static error if an implementation is unable to process a schema or module import by finding a schema or module with the specified target namespace.
It is a static error if the name of a function in a function declaration is not in a namespace (expanded QName has an empty URI).
It is a dynamic error if validity assessment is performed on a document node unless the children of the document node comprise exactly one element node, no text nodes, and zero or more comment and processing instruction nodes, in any order.
It is a dynamic error if a document-level constraint is not satisfied when validity assessment is performed on a document node. Document-level constraints include identity constraints (xs:unique
, xs:key
, and xs:keyref
) and ID/IDREF constraints.
It is a static error if the URI specified by a default function namespace declaration is a zero-length string.
It is a dynamic error if the value of the name expression in a computed processing instruction constructor is equal to "XML" (in any combination of upper and lower case).
A static error is raised if a Prolog contains more than one ordering mode declaration.
A static error is raised if a Prolog contains more than one default element/type namespace declaration, or more than one default function namespace declaration.
A static error is raised if a Prolog contains more than one construction declaration.
A static error is raised if a Prolog contains more than one Xmlspace declaration.
A static error is raised if a Prolog contains more than one empty ordering declaration.
A static error is raised if the predefined namespace prefix xml
or xmlns
is redeclared by a namespace declaration or namespace declaration attribute.
A static error is raised if the namespace declaration attributes of a direct element constructor do not have distinct names.
It is a dynamic error if the result of the content expression of a computed comment constructor contains two adjacent hyphens or ends with a hyphen.
It is a static error if the graph of module imports contains a cycle (that is, if there exists a sequence of modules M1 ... Mn such that each Mi imports Mi+1 and Mn imports M1.)
It is a dynamic error if the value of the name expression in a computed element constructor cannot be converted to an expanded QName (for example, because it contains a namespace prefix not found in statically known namespaces.
An atomic value is a value in the value space of an atomic type, including all the atomic types defined in [XML Schema], and three additional atomic types: xdt:dayTimeDuration, xdt:yearMonthDuration, and xdt:untypedAtomic.
Atomization of a sequence is defined as the result of invoking the fn:data
function on the sequence, as defined in [XQuery 1.0 and XPath 2.0 Functions and Operators].
Available collections. This is a mapping of strings onto sequences of nodes. The string represents the absolute URI of a resource. The sequence of nodes represents the result of the fn:collection
function when that URI is supplied as the argument.
Available documents. This is a mapping of strings onto document nodes. The string represents the absolute URI of a resource. The document node is the root of a tree that represents that resource using the data model. The document node is returned by the fn:doc
function when applied to that URI.
Base URI. This is an absolute URI, used when necessary in the resolution of relative URIs (for example, by the fn:resolve-uri
function.)
A base URI declaration specifies the base URI property of the static context, which is used when resolving relative URIs within a module.
The value of the expression associated with a variable in a for
clause is called the binding sequence for that variable.
Whitespace characters that occur by themselves in the boundaries between tags and/or enclosed expressions are called boundary whitespace.
The built-in functions supported by XQuery are defined in [XQuery 1.0 and XPath 2.0 Functions and Operators].
A collation is a specification of the manner in which character strings are compared and, by extension, ordered. For a more complete definition of collation, see [XQuery 1.0 and XPath 2.0 Functions and Operators].
One way to construct a sequence is by using the comma operator, which evaluates each of its operands and concatenates the resulting sequences, in order, into a single result sequence.
A computed element constructor creates an element node, allowing both the name and the content of the node to be computed.
A construction declaration sets the construction mode in the static context, overriding any implementation-provided default.
Construction mode. The construction mode governs the behavior of element constructors. If construction mode is preserve
, the type of a constructed element node is xs:anyType
, and the attributes and descendants of the constructed element retain their original types. If construction mode is strip
, the type of the constructed element node and all its descendants is xdt:untyped
, and attributes of the constructed element have type
xdt:untypedAtomic
.
The context item is the item currently being processed. An item is either an atomic value or a node.
When the context item is a node, it can also be referred to as the context node.
The context position is the position of the context item within the sequence of items currently being processed.
The context size is the number of items in the sequence of items currently being processed.
Current dateTime. This information represents an implementation-dependent point in time during the processing of a query, and includes an explicit timezone. It can be retrieved by the fn:current-dateTime
function. If invoked multiple times during the execution of a query, this function always returns the same result.
XQuery operates on the abstract, logical structure of an XML document, rather than its surface syntax. This logical structure, known as the data model, is defined in the [XQuery 1.0 and XPath 2.0 Data Model] document.
The term data model instance is used, synonymously with the term value, to denote an unconstrained sequence of nodes and/or atomic values.
For a given node in a data model instance, the data model schema is defined as the schema from which the type annotation of that node was derived.
Default collation. This identifies one of the collations in statically known collations as the collation to be used by string comparison functions and operators when no explicit collation is specified.
A default collation declaration sets the value of the default collation in the static context, overriding any implementation-provided default.
Default collection. This is the sequence of nodes that would result from calling the fn:collection
function with no arguments.
Default element/type namespace. This is a namespace URI or "none". The namespace URI, if present, is used for any unprefixed QName appearing in a position where an element or type name is expected.
Default function namespace. This is a namespace URI that is used for any unprefixed QName appearing as the function name in a function call. The initial default function namespace may be provided by the external environmentor by a declaration in a Prolog.
Default ordering for empty sequences. This component controls whether an empty sequence is interpreted as the greatest value or as the least value during processing of an order by
clause in a FLWOR expression, as described in 3.8.3 Order By and Return Clauses.
A delimiting terminal may delimit adjacent non-delimiting terminals.
A direct element constructor is a form of element constructor in which the name of the constructed element is a constant.
Informally, document order is the order in which nodes appear in the XML serialization of a document.
The dynamic context of an expression is defined as information that is available at the time the expression is evaluated.
A dynamic error is an error that must be detected during the evaluation phase and may be detected during the analysis phase. Numeric overflow is an example of a dynamic error.
The dynamic evaluation phase is the phase during which the value of an expression is computed.
Each atomic value, element node, and attribute node in a data model instance has a dynamic type. The dynamic type specifies a range of values—for example, an attribute named version
might have the dynamic type xs:decimal
, indicating that it contains a decimal value.
The effective boolean value of a value is defined as the result of applying the fn:boolean
function to the value, as defined in [XQuery 1.0 and XPath 2.0 Functions and Operators].
The effective case in a typeswitch
expression is the first case
clause such that the value of the operand expression matches the SequenceType in the case
clause, using the rules of SequenceType matching.
An empty ordering declaration sets the default ordering for empty sequences in the static context, which controls whether an empty sequence is interpreted as the greatest value or as the least value during processing of an order by
clause in a FLWOR expression.
A sequence containing zero items is called an empty sequence.
If present, a version declaration may optionally include an encoding declaration. The purpose of an encoding declaration is to allow the writer of a query to provide a string that indicates how the query is encoded, such as "utf-8
", "utf-16
", or "us-ascii
".
An expanded QName consists of an optional namespace URI and a local name. An expanded QName also retains its original namespace prefix (if any), to facilitate casting the expanded QName into a string.
The expression context for a given expression consists of all the information that can affect the result of the expression.
External functions are functions that are implemented outside the query environment.
The first three components of the dynamic context (context item, context position, and context size) are called the focus of the expression.
An XQuery implementation that supports the Full Axis Feature must support all the optional axes.
XQuery is a functional language, which means that expressions can be nested with full generality. (However, unlike a pure functional language, it does not allow variable substitutability if the variable declaration contains construction of new nodes.)
Function implementations. Each function in function signatures has a function implementation that enables the function to map instances of its parameter types into an instance of its result type. For a user-defined function, the function implementation is an XQuery expression. For a built-in function or external function, the function implementation is implementation-dependent.
Function signatures. This component defines the set of functions that are available to be called from within an expression. Each function is uniquely identified by its expanded QName and its arity (number of parameters).
In the operator mapping tables, the term Gregorian refers to the types xs:gYearMonth
, xs:gYear
, xs:gMonthDay
, xs:gDay
, and xs:gMonth
.
Unless otherwise specified (see A.2.2.2 Explicit Whitespace Handling), Ignorable whitespace may occur between terminals, and is not significant to the parse tree. For readability, whitespace may be used in most expressions even though not explicitly notated in the EBNF. All allowable whitespace that is not explicitly specified in the EBNF is ignorable whitespace, and converse, this term does not apply to whitespace that is explicitly specified.
Implementation-defined indicates an aspect that may differ between implementations, but must be specified by the implementor for each particular implementation.
Implementation-dependent indicates an aspect that may differ between implementations, is not specified by this or any W3C specification, and is not required to be specified by the implementor for any particular implementation.
Implicit timezone. This is the timezone to be used when a date, time, or dateTime value that does not have a timezone is used in a comparison or arithmetic operation. The implicit timezone is an implementation-defined value of type xdt:dayTimeDuration
. See [ISO 8601] for the range of legal values of a timezone.
An inherit-namespaces declaration sets the value of namespace inheritance mode in the static context, overwriting any implementation-provided default. Namespace inheritance mode controls the namespace bindings that are inherited when an existing element node is copied by an element constructor.
If a variable declaration includes an expression, the expression is called an initializing expression.
In-scope attribute declarations. Each attribute declaration is identified either by an expanded QName (for a top-level attribute declaration) or by an implementation-dependent attribute identifier (for a local attribute declaration). If the Schema Import Feature is supported, in-scope attribute declarations include all attribute declarations found in imported schemas.
In-scope element declarations. Each element declaration is identified either by an expanded QName (for a top-level element declaration) or by an implementation-dependent element identifier (for a local element declaration). If the Schema Import Feature is supported, in-scope element declarations include all element declarations found in imported schemas.
The in-scope namespaces property of an element node is a set of namespace bindings, each of which associates a namespace prefix with a URI, thus defining the set of namespace prefixes that are available for interpreting QNames within the scope of the element. For a given element, one namespace binding may have an empty prefix; the URI of this namespace binding is the default namespace within the scope of the element.
In-scope schema definitions. This is a generic term for all the element, attribute, and type definitions that are in scope during processing of an expression.
In-scope type definitions. Each type definition is identified either by an expanded QName (for a named type) or by an implementation-dependent type identifier (for an anonymous type). The in-scope type definitions include the predefined types described in 2.5.1 Predefined Types. If the Schema Import Feature is supported, in-scope type definitions also include all type definitions found in imported schemas.
In-scope variables. This is a set of (expanded QName, type) pairs. It defines the set of variables that are available for reference within an expression. The expanded QName is the name of the variable, and the type is the static type of the variable.
An item is either an atomic value or a node.
An alternative form of a node test called a kind test can select nodes based on their kind, name, and type annotation.
A module that does not contain a Query Body is called a library module. A library module consists of a module declaration followed by a Prolog.
A literal is a direct syntactic representation of an atomic value.
A main module consists of a Prolog followed by a Query Body.
A module is a fragment of XQuery code that conforms to the Module grammar and can independently undergo the static analysis phase described in 2.2.3 Expression Processing. Each module is either a main module or a library module.
A module declaration serves to identify a module as a library module. A module declaration consists of the keyword module
followed by a namespace prefix and a string literal which must contain a valid URI. [err:XQ0046]
An XQuery implementation that does not support the Module Feature raises a static error [err:XQ0016] if it encounters a module declaration or a module import.
A module import imports the function declarations and variable declarations from one or more library modules into the function signatures and in-scope variables of the importing module.
An implementation may extend XQuery functionality by supporting must-understand extensions.
A namespace declaration declares a namespace prefix and associates it with a namespace URI, adding the (prefix, URI) pair to the set of statically known namespaces.
A namespace declaration attribute is used inside a direct element constructor. Its purpose is to bind a namespace prefix or to set the default element/type namespace for the constructed element node, including its attributes.
Namespace inheritance mode. This component controls the namespace bindings that are inherited when an existing element node is copied by an element constructor, as described in 3.7.1 Direct Element Constructors. Its value may be yes
or no
.
A node test that consists only of a QName or a Wildcard is called a name test.
A node is an instance of one of the node kinds defined in [XQuery 1.0 and XPath 2.0 Data Model].
A node test is a condition that must be true for each node selected by a step.
Non-delimiting terminals generally start and end with alphabetic characters or digits. Adjacent non-delimiting terminals must be delimited by a delimiting terminal.
When referring to a type, the term numeric denotes the types xs:integer
, xs:decimal
, xs:float
, and xs:double
.
A predicate whose predicate expression returns a numeric type is called a numeric predicate.
Under certain circumstances, an atomic value can be promoted from one type to another. Numeric type promotion is used in function calls (see 3.1.5 Function Calls) and in processing of operators that accept numeric operands (see B.2 Operator Mapping).
For each operator and valid combination of operand types, the operator mapping tables specify a result type and an operator function that implements the semantics of the operator for the given types.
The following axes are designated as optional axes: ancestor
, ancestor-or-self
, following
, following-sibling
, preceding
, and preceding-sibling
.
Ordering mode. Ordering mode, which has the value ordered
or unordered
, affects the ordering of the result sequence returned by path expressions, union
, intersect
, and except
expressions, and FLWOR expressions that have no order by
clause.
An ordering mode declaration sets the ordering mode in the static context, overriding any implementation-defined default.
A pragma may be used to provide additional information to an XQuery implementation.
A predicate consists of an expression, called a predicate expression, enclosed in square brackets. A predicate serves to filter a sequence, retaining some items and discarding others.
Primary expressions are the basic primitives of the language. They include literals, variable references, context item expressions, constructors, and function calls. A primary expression may also be created by enclosing any expression in parentheses, which is sometimes helpful in controlling the precedence of operators.
Every axis has a principal node kind. If an axis can contain elements, then the principal node kind is element; otherwise, it is the kind of nodes that the axis can contain.
A production combines symbols to form more complex patterns.
A Prolog is a series of declarations and imports that define the processing environment for the module that contains the Prolog.
Lexically, a QName consists of an optional namespace prefix and a local name. If the namespace prefix is present, it is separated from the local name by a colon.
The Query Body, if present, consists of an expression that defines the result of the query.
The node ordering that is the reverse of document order is called reverse document order.
A schema import imports the element, attribute, and type definitions from a schema into the in-scope schema definitions.
If the Schema Import Feature is supported, a Prolog may contain a schema import. Definitions from the imported schema are added to the in-scope schema definitions.
A sequence is an ordered collection of zero or more items.
When it is necessary to refer to a type in an XQuery expression, the SequenceType syntax is used. The name SequenceType suggests that this syntax is used to describe the type of an XQuery value, which is always a sequence.
During evaluation of an expression, it is sometimes necessary to determine whether a value with a known type "matches" an expected type, expressed in the SequenceType syntax. This process is known as SequenceType matching.
Serialization is the process of converting a data model instance into a sequence of octets (step DM4 in Figure 1.)
The first part of the Prolog consists of declarations that are called setters because they set the value of some property that affects query processing, such as construction mode, ordering mode, or default collation.
A sequence containing exactly one item is called a singleton sequence.
Document order is stable, which means that the relative order of two nodes will not change during the processing of a given query, even if this order is implementation-dependent.
Statically known collations. This is a set of (URI, collation) pairs. It defines the names of the collations that are available for use in function calls that take a collation name as an argument.
Statically known collections. This is a mapping from strings onto types. The string represents the absolute URI of a resource that is potentially available using the fn:collection
function. The type is the type of the sequence of nodes that would result from calling the fn:collection
function with this URI as its argument.
Statically known default collection type. This is the type of the sequence of nodes that would result from calling the fn:collection
function with no arguments.
Statically known documents. This is a mapping from strings onto types. The string represents the absolute URI of a resource that is potentially available using the fn:doc
function. The type is the static type of a call to fn:doc
with the given URI as its literal argument.
Statically known namespaces. This is a set of (prefix, URI) pairs that define all the namespaces that are known during static processing of a given expression.
The static analysis phase depends on the expression itself and on the static context. The static analysis phase does not depend on input data (other than schemas).
The static context of an expression is the information that is available during static analysis of the expression, prior to its evaluation.
A static error is an error that must be detected during the analysis phase. A syntax error is an example of a static error. The means by which static errors are reported during the analysis phase is implementation-defined.
The static type of an expression may be either a named type or a structural description—for example, xs:boolean?
denotes an optional occurrence of the xs:boolean
type. The rules for inferring the static types of various expressions are described in [XQuery 1.0 and XPath 2.0 Formal Semantics].
A static typing extension is a type inference rule that infers a more precise static type than that inferred by the type inference rules in [XQuery 1.0 and XPath 2.0 Formal Semantics].
An XQuery implementation that supports the Static Typing Feature is required to detect and raise type errors during the static analysis phase.
The string value of a node is a string and can be extracted by applying the fn:string
function to the node.
XQuery is also a strongly-typed language in which the operands of various expressions, operators, and functions must conform to the expected types.
Substitution groups are defined in [XML Schema] Part 1, Section 2.2.2.2. Informally, the substitution group headed by a given element (called the head element) consists of the set of elements that can be substituted for the head element without affecting the outcome of schema validation.
The use of a value whose actual type is derived from the expected type is known as subtype substitution.
Each rule in the grammar defines one symbol, in the form
Each imported schema or module is identified by its target namespace, which is the namespace of the objects (such as elements or functions) that are defined by the schema or module.
A terminal is a single unit of the grammar that can not be further subdivided, and is specified in the EBNF by a character or characters in quotes, or a regular expression.
The type annotation of an element or attribute node is an implementation-dependent representation of its dynamic type.
The typed value of a node is a sequence of atomic values and can be extracted by applying the fn:data
function to the node.
A type error may be raised during the analysis or evaluation phase. During the analysis phase, a type error occurs when the static type of an expression does not match the expected type of the context in which the expression occurs. During the evaluation phase, a type error occurs when the dynamic type of a value does not match the expected type of the context in which the value occurs.
For a user-defined function, the function declaration includes an expression called the function body that defines how the result of the function is computed from its parameters.
In the data model, a value is always a sequence.
A variable reference is a QName preceded by a $-sign.
Variable values. This is a set of (expanded QName, value) pairs. It contains the same expanded QNames as the in-scope variables in the static context for the expression. The expanded QName is the name of the variable and the value is the dynamic value of the variable, which includes its dynamic type.
Any module may contain a version declaration. If present, the version declaration occurs at the beginning of the module and identifies the applicable XQuery syntax and semantics for the module.
Whitespace characters are defined by [http://www.w3.org/TR/REC-xml#NT-S] when these characters occur outside of a StringLiteral.
xdt:anyAtomicType
includes all atomic values (and no values that are not atomic).
xdt:dayTimeDuration
is derived by restriction from xs:duration
. The lexical representation of xdt:dayTimeDuration
is restricted to contain only day, hour, minute, and second components.
xdt:untyped
is used to denote the dynamic type of an element node that has not been validated, or has been validated in skip
mode.
xdt:untypedAtomic
is used to denote untyped atomic data, such as text that has not been assigned a more specific type.
xdt:yearMonthDuration
is derived by restriction from xs:duration
. The lexical representation of xdt:yearMonthDuration
is restricted to contain only year and month components.
An XQuery implementation may choose to support either [XML 1.0] and [XML Names], or alternatively, [XML 1.1] and [XML Names 1.1]. An implementation that supports the latter pair of specifications is said to support the XML and Names 1.1 Feature.
An xmlspace declaration sets the XMLSpace policy in the static context, overriding any implementation-provided default. XMLSpace policy controls whether boundary whitespace is preserved by element constructors during processing of the query.
XMLSpace policy. This component controls the processing of whitespace by element constructors, as described in 3.7.1.4 Whitespace in Element Content.
XPath 1.0 compatibility mode. This component must be set by all host languages that include XPath 2.0 as a subset, indicating whether rules for compatibility with XPath 1.0 are in effect. XQuery sets the value of this component to false
.
An XQuery Flagger is a facility that is provided by an implementation that is able to identify queries that contain must-understand extensions. If an implementation supports must-understand extensions, then an XQuery Flagger must be provided.
An XQuery Static Flagger is a facility that is able to identify queries that require a static typing extension.
This section contains examples of several important classes of queries that can be expressed using XQuery. The applications described here include joins across multiple data sources, grouping and aggregation, queries based on sequential relationships, recursive transformations, and selection of distinct combinations of values.
Joins, which combine data from multiple sources into a single result, are a very important type of query. In this section we will illustrate how several types of joins can be expressed in XQuery. We will base our examples on the following three documents:
A document named parts.xml
that contains many part
elements; each part
element in turn contains partno
and description
subelements.
A document named suppliers.xml
that contains many supplier
elements; each supplier
element in turn contains suppno
and suppname
subelements.
A document named catalog.xml
that contains information about the relationships between suppliers and parts. The catalog document contains many item
elements, each of which in turn contains partno
, suppno
, and price
subelements.
A conventional ("inner") join returns information from two or more related sources, as illustrated by the following example, which combines information from three documents. The example generates a "descriptive catalog" derived from the catalog document, but containing part descriptions instead of part numbers and supplier names instead of supplier numbers. The new catalog is ordered alphabetically by part description and secondarily by supplier name.
<descriptive-catalog> { for $i in fn:doc("catalog.xml")/items/item, $p in fn:doc("parts.xml")/parts/part[partno = $i/partno], $s in fn:doc("suppliers.xml")/suppliers /supplier[suppno = $i/suppno] order by $p/description, $s/suppname return <item> { $p/description, $s/suppname, $i/price } </item> } </descriptive-catalog>
The previous query returns information only about parts that have suppliers and suppliers that have parts. An outer join is a join that preserves information from one or more of the participating sources, including elements that have no matching element in the other source. For example, a left outer join between suppliers and parts might return information about suppliers that have no matching parts.
The following query demonstrates a left outer join. It returns names of all the suppliers in alphabetic order, including those that supply no parts. In the result, each supplier element contains the descriptions of all the parts it supplies, in alphabetic order.
for $s in fn:doc("suppliers.xml")/suppliers/supplier order by $s/suppname return <supplier> { $s/suppname, for $i in fn:doc("catalog.xml")/items/item [suppno = $s/suppno], $p in fn:doc("parts.xml")/parts/part [partno = $i/pno] order by $p/description return $p/description } </supplier>
The previous query preserves information about suppliers that supply no parts. Another type of join, called a full outer join, might be used to preserve information about both suppliers that supply no parts and parts that have no supplier. The result of a full outer join can be structured in any of several ways. The following query generates a list of supplier
elements, each containing nested part
elements for the parts that it supplies (if any), followed by a list of
part
elements for the parts that have no supplier. This might be thought of as a "supplier-centered" full outer join. Other forms of outer join queries are also possible.
<master-list> { for $s in fn:doc("suppliers.xml")/suppliers/supplier order by $s/suppname return <supplier> { $s/suppname, for $i in fn:doc("catalog.xml")/items/item [suppno = $s/suppno], $p in fn:doc("parts.xml")/parts/part [partno = $i/partno] order by $p/description return <part> { $p/description, $i/price } </part> } </supplier> , (: parts that have no supplier :) <orphan-parts> { for $p in fn:doc("parts.xml")/parts/part where fn:empty(fn:doc("catalog.xml")/items/item [partno = $p/partno] ) order by $p/description return $p/description } </orphan-parts> } </master-list>
The previous query uses an element constructor to enclose its output inside a master-list
element. The concatenation operator (",") is used to combine the two main parts of the query. The result is an ordered sequence of supplier
elements followed by an orphan-parts
element that contains descriptions of all the parts that have no supplier.
Many queries involve forming data into groups and applying some aggregation function such as fn:count
or fn:avg
to each group. The following example shows how such a query might be expressed in XQuery, using the catalog document defined in the previous section.
This query finds the part number and average price for parts that have at least 3 suppliers.
for $pn in fn:distinct-values( fn:doc("catalog.xml")/items/item/partno) let $i := fn:doc("catalog.xml")/items/item[partno = $pn] where fn:count($i) >= 3 order by $pn return <well-supplied-item> <partno> {$p} </partno> <avgprice> {fn:avg($i/price)} </avgprice> </well-supplied-item>
The fn:distinct-values
function in this query eliminates duplicate part numbers from the set of all part numbers in the catalog document. The result of fn:distinct-values
is a sequence in which order is not significant.
Note that $pn
, bound by a for clause, represents an individual part number, whereas $i
, bound by a let clause, represents a set of items which serves as argument to the aggregate functions fn:count($i)
and fn:avg($i/price)
. The query uses an element constructor to enclose each part number and average price in a containing element called well-supplied-item
.
The method illustrated above generalizes easily to grouping by more than one data value. For example, consider a census document containing a sequence of person
elements, each with subelements named state
, job
, and income
. A census analyst might need to prepare a report listing the average income
for each combination of state
and job
. This report might be produced using the following query:
for $s in fn:distinct-values( fn:doc("census.xml")/census/person/state), $j in fn:distinct-values( fn:doc("census.xml")/census/person/job) let $p := fn:doc("census.xml")/census/person [state = $s and job = $j] order by $s, $j return if (fn:exists($p)) then <group> <state> {$s} </state> <job> {$j} </job> <avgincome> {fn:avg($p/income)} </avgincome> </group> else ()
The if-then-else
expression in the above example prevents generation of groups that contain no data. For example, the census data may contain some persons who live in Nebraska, and some persons whose job is Deep Sea Fisherman, but no persons who live in Nebraska and have the job of Deep Sea Fisherman. If output groups are desired for all possible combinations of states and jobs, the if-then-else
expression can be omitted from the query. In this case, the output may include
"empty" groups such as the following:
<group> <state>Nebraska</state> <job>Deep Sea Fisherman</state> <avgincome/> </group>
XQuery uses the <<
and >>
operators to compare nodes based on document order. Although these operators are quite simple, they can be used to express complex queries for XML documents in which sequence is meaningful. The first two queries in this section involve a surgical report that contains procedure
, incision
, instrument
, action
, and anesthesia
elements.
The following query returns all the action
elements that occur between the first and second incision
elements inside the first procedure. The original document order among these nodes is preserved in the result of the query.
let $proc := /report/procedure[1] for $i in $proc//action where $i >> ($proc//incision)[1] and $i << ($proc//incision)[2] return $i
It is worth noting here that document order is defined in such a way that a node is considered to precede its descendants in document order. In the surgical report, an action
is never part of an incision
, but an instrument
is. Since the >>
operator is based on document order, the predicate $i >> ($proc//incision)[1]
is true for any instrument
element that is a descendant of the first incision
element
in the first procedure.
For some queries, it may be helpful to define a function that can test whether a node precedes another node without being its ancestor. The following function returns true
if its first operand precedes its second operand but is not an ancestor of its second operand; otherwise it returns false
:
declare function local:precedes($a as node(), $b as node()) as boolean { $a << $b and fn:empty($a//node() intersect $b) };
Similarly, a local:follows
function could be written:
declare function local:follows($a as node(), $b as node()) as boolean { $a >> $b and fn:empty($b//node() intersect $a) };
Using the local:precedes
function, we can write a query that finds instrument
elements between the first two incisions, excluding from the query result any instrument
that is a descendant of the first incision
:
let $proc := /report/procedure[1] for $i in $proc//instrument where local:precedes(($proc//incision)[1], $i) and local:precedes($i, ($proc//incision)[2]) return $i
The following query reports incisions for which no prior anesthesia was recorded in the surgical report. Since an anesthesia
is never part of an incision
, we can use <<
instead of the less-efficient local:precedes
function:
for $proc in /report/procedure where some $i in $proc//incision satisfies fn:empty($proc//anesthesia[. << $i]) return $proc
In some documents, particular sequences of elements may indicate a logical hierarchy. This is most commonly true of HTML. The following query returns the introduction of an XHTML document, wrapping it in a div
element. In this example, we assume that an h2
element containing the text "Introduction" marks the beginning of the introduction, and the introduction continues until the next h2
or h1
element, or the end of the document, whichever comes
first.
let $intro := //h2[text()="Introduction"], $next-h := //(h1|h2)[. >> $intro][1] return <div> { $intro, if (fn:empty($next-h)) then //node()[. >> $intro] else //node()[. >> $intro and . << $next-h] } </div>
Note that the above query makes explicit the hierarchy that was implicit in the original document. In this example, we assume that the h2
element containing the text "Introduction" has no subelements.
Occasionally it is necessary to scan over a hierarchy of elements, applying some transformation at each level of the hierarchy. In XQuery this can be accomplished by defining a recursive function. In this section we will present two examples of such recursive functions.
Suppose that we need to compute a table of contents for a given document by scanning over the document, retaining only elements named section
or title
, and preserving the hierarchical relationships among these elements. For each section
, we retain subelements named section
or title
; but for each title
, we retain the full content of the element. This might be accomplished by the following recursive function:
declare function local:sections-and-titles($n as node()) as node()? { if (fn:local-name($n) = "section") then element { fn:local-name($n) } { for $c in $n/* return local:sections-and-titles($c) } else if (fn:local-name($n) = "title") then $n else ( ) };
The "skeleton" of a given document, containing only its sections and titles, can then be obtained by invoking the local:sections-and-titles
function on the root node of the document, as follows:
local:sections-and-titles(fn:doc("cookbook.xml"))
As another example of a recursive transformation, suppose that we wish to scan over a document, transforming every attribute named color
to an element named color
, and every element named size
to an attribute named size
. This can be accomplished by the following recursive function:
declare function local:swizzle($n as node()) as node() { typeswitch($n) case $a as attribute(color) return element color { fn:string($a) } case $es as element(size) return attribute size { fn:string($es) } case $e as element() return element { fn:local-name($e) } { for $c in $e/(* | @*) return local:swizzle($c) } case $d as document-node() return document { for $c in $d/* return local:swizzle($c) } default return $n };
The transformation can be applied to a whole document by invoking the local:swizzle
function on the root node of the document, as follows:
local:swizzle(fn:doc("plans.xml"))
It is sometimes necessary to search through a set of data to find all the distinct combinations of a given list of properties. For example, an input data set might consist of a large set of order
elements, each of which has the same basic structure, as illustrated by the following example:
<order> <date>2003-10-15</date> <product>Dress Shirt</product> <size>M</size> <color>Blue</color> <supplier>Fashion Trends</supplier> <quantity>50</quantity> </order>
From this data set, a user might wish to find all the distinct combinations of product
, size
, and color
that occur together in an order
. The following query returns this list, enclosing each distinct combination in a new element named option
:
for $p in fn:distinct-values(/orders/order/product), $s in fn:distinct-values(/orders/order/size), $c in fn:distinct-values(/orders/order/color) order by $p, $s, $c return if (fn:exists(/orders/order[product eq $p and size eq $s and color eq $c])) then <option> <product>{$p}</product> <size>{$s}</size> <color>{$c}</color> </option> else ()
application/xquery
Media Type (Non-Normative)This Appendix specifies the media type for XQuery Version 1.0. XQuery is a language for querying over collections of data from XML data sources, as specified in the main body of this document.
This document, together with its normative references, defines the language XQuery Version 1.0. This Appendix provides information about the application/xquery
media type, which is intended to be used for transmitting queries written in the XQuery language.
This document was prepared by members of the W3C XML Query Working Group. Please send comments to public-qt-comments@w3.org, a public mailing list with archives at http://lists.w3.org/Archives/Public/public-qt-comments.
application/xquery
MIME media type name: application
MIME subtype name: xquery
Required parameters: none
Optional parameters: charset
The syntax of XQuery is expressed in Unicode but may be written with any Unicode-compatible character encoding, including UTF-8 or UTF-16, or transported as US-ASCII or Latin-1 with Unicode characters outside the range of the given encoding represented using an XML-style ෝ
syntax.
The public XQuery Web page lists more than two dozen implementations of the XQuery language, both proprietary and open source.
This new media type is being registered to allow for deployment of XQuery on the World Wide Web.
The most common file extensions in use for XQuery are .xq
and .xquery
.
The appropriate Macintosh file type code is TEXT
.
For use with transports that are not 8-bit clean, quoted-printable encoding is recommended since the XQuery syntax itself uses the US-ASCII-compatible subset of Unicode.
An XQuery document may contain an encoding declaration as part of its version declaration:
xquery version "1.0" encoding "utf-8";
If an XQuery document contains an encoding declaration, it overrides the default encoding specified by the MIME charset
parameter.
An XQuery file may have the string xquery version "V.V"
near the beginning of the document, where "V.V"
is a version number. Currently the version number, if present, must be "1.0"
.
XQuery documents use the Unicode character set and, by default, the UTF-8 encoding.
Queries written in XQuery may cause arbitrary URIs to be dereferenced. Therefore, the security issues of [Uniform Resource Locators (URL)] Section 6 should be considered. In addition, the contents of file:
URIs can in some cases be accessed, processed and returned as results.
Furthermore, because the XQuery language permits extensions, it is possible that application/xquery
may describe content that has security implications beyond those described here.
The XML Query Working group is working on a facility to allow XQuery expressions to be used to create and update persistent data. Untrusted queries should not be given write access to data.
This log records the changes that have been made to this document since the Last Call Draft of 12 November 2003.
An ordering
declaration has been added to the Prolog, which affects the ordering semantics of path expressions, FLWOR expressions, and union
, intersect
, and except
expressions. In addition, ordered
and unordered
operators have been introduced that permit ordering semantics to be controlled at the expression level within a query.
The SequenceType syntax has been simplified. SchemaContextPath is no longer part of the SequenceType syntax. Also, the section on SequenceType Matching has been rewritten to make its terminology more consistent with the Formal Semantics document.
Validation has been separated from construction. Validation now occurs only as a result of an explicit validate
expression. Validation modes are strict
and lax
, and are specified on the validate
expression. New construction modes strip
and preserve
have been defined and are declared in the Prolog. The notion of "validation context" has been deleted. The XQuery definition of validation has been converged with the definition
used in XSLT.
It is now permitted for multiple user-defined functions to have the same name as long as they have different numbers of arguments.
The term xdt:untypedAny
is changed to xdt:untyped
.
xs:anyType
is no longer an abstract type, but is now used to denote the type of a partially validated element node. Since there is no longer a meaningful distinction between abstract types and concrete types, these terms are no longer used in this document.
Value comparisons now return ()
if either operand is ()
.
Computed namespace constructors are now completely static and are allowed only inside a computed element constructor. Namespace declarations in a computed element constructor must come before the element content, and must consist entirely of literals. The namespace prefix is optional. If absent, it has the effect of setting the default namespace for elements and types within the scope of the constructed element.
The name of the Predicates grammar production has been changed to PredicateList.
Grammar changes have been made in the Prolog, including constraints on the order of declarations and imports.
The grammar production formerly called a FilterStep is now called a FilterExpression and is described in a separate section rather than as part of a path expression.
The precedence of the cast
and treat
operators in the grammar has been increased.
The precedence of unary arithmetic operators has been increased.
The syntax for variable initialization in the Prolog now uses an assignment operator (":=
"). Also, circularities in variable initialization are now considered to be a static errors.
The appendix containing a list of error messages has been made non-normative.
An error is raised if a module attempts to import itself (target namespace of importing module and imported modules are the same).
A schema can now be imported without specifying either a target namespace or a location hint.
Module imports and schema imports now accept multiple location hints, representing multiple physical resources in the same module or schema.
CData Sections are no longer considered to be constructors, but are simply a notational convenience for embedding special characters in the content of an element or attribute constructor.
Three new components have been added to the static context: XQuery Flagger status, XQuery Static Flagger status, and context item static type.
The expression data(())
no longer raises a static error, although its static type is empty.
If a dynamic implementation detects a static error, the evaluation phase is optional.
XPath allows host languages to specify whether they recognize the concept of a namespace node. XQuery does not recognize namespace nodes. Instead, it recognizes an "in-scope namespaces" property of an element node.
The specification now clearly distinguishes between "statically-known namespaces" (a static property of an expression) and "in-scope namespaces" (a dynamic property of an element).
An order by
clause may now accept values of mixed type if they have a common type that is reachable by numeric type promotion and/or moving up the type derivation hierarchy, and if this common type has a gt
operator.
In element and document node constructors, if the content sequence contains a document node, that node is replaced by its children (this was previously treated as an error).
Atomization now applies to the name expression of a computed processing instruction constructor.
It is now implementation-defined whether undeclaration of namespace prefixes in an element constructor is supported. If supported, this feature conforms to the semantics of Namespaces 1.1. In other words, if an element constructor binds a namespace prefix to the zero-length string, any binding of that prefix defined at an outer level is suspended within the scope of the constructed element.
The names of certain components in the static and dynamic contexts have been changed to make them more consistent and descriptive.
In a computed text node constructor, the expression enclosed in curly braces is no longer optional, since it is not possible to construct an empty text node.
The definition of the idiv
operator has been made consistent with the Functions and Operators document. The idiv
operator accepts operands of any numeric types, performs a division, and truncates the result to an integer.
Certain grammar productions have been renamed and reordered to make the grammar easier to read.
The section on constructor functions has been edited to make it more consistent with the definition of constructor functions in the Functions and Operators document.
The Comments section has been moved out of the Primary Expressions section, because a comment is not a primary expression.
Rules for processing comment constructors have changed, to ensure that the resulting comment does not contain adjacent hyphens or end with a hyphen.
Some additional constraints have been added to the section titled "Consistency Constraints".
Various minor changes, both editorial and substantive, have been made in response to public comments and working group discussions.
The last step in a path expression is now allowed to return a sequence of atomic values or a sequence of nodes (mixed nodes and atomic values are not allowed.)
A value of type xs:QName is now defined to consist of a "triple": a namespace prefix, a namespace URI, and a local name. Including the prefix as part of the QName value makes it possible to cast any QName into a string when needed.
Local namespace declarations have been deleted from computed element constructors. No namespace bindings may be declared by a computed element constructors. Also, the body of a computed element constructor has changed from ExprSingle to Expr.
The Prolog has been reorganized into three parts which must appear in this order: (a) Setters; (b) Namespace declarations and module and schema imports; (c) function and variable declarations.
A new "inherit-namespaces" declaration has been added to the Prolog, and "namespace inheritance mode" has been added to the static context.
An "encoding" subclause has been added to the Version Declaration in the Prolog.
A new declaration has been added to the Prolog to control the query-wide default handling of empty sequences in ordering keys ("empty greatest" or "empty least".) "Default ordering for empty sequence" has been added to static context.
XQuery Processing Model figure has been revised to include a reference to modules.
The expression in the where-clause of a FLWOR expression has changed from Expr to ExprSingle.
Clarification: The same variable name may be bound in more than one for or let clause in a given FLWOR expression. This is not an error, but each new binding occludes the previous one, which is no longer accessible in the rest of the FLWOR expression.
In the static context, "current date" and "current time" have been replaced by "current dateTime", which is defined to include a timezone. Also, an implementation is required to initialize the current dateTime and implicit timezone.
Computed comment constructors now raise an error rather than trying to "fix up" an invalid comment by inserting blanks.
The div
operator can now be used to divide two yearMonthDurations or two dayTimeDurations. In either case, the result is of type xs:decimal
.
Additional signatures have been added to the fn:error
function.
The to
operator now accepts an empty sequence as an operand, and returns empty sequence.
Support for XML 1.1 and Namespaces 1.1 have been bundled together and defined as an optional feature. Various aspects of query processing and serialization that depend on this optional feature have been identified.
Descriptions of the arithmetic and logical operators have been edited to eliminate dependencies on the order of operand evaluation.
The term "module resource," originally defined as a fragment of XQuery code that can independently undergo static analysis, has been replaced by the term "module."
Cyclic module imports are no longer permitted. A module M may not import another module that directly or indirectly imports module M.
A new zero-argument version of fn:collection
has been defined, to provide access to an implementation-defined default sequence.
A Mime encoding (application/xquery) has been defined for XQuery, and a new Appendix has been added to describe it.
The operator mapping for numeric ge
and le
operators has been changed.
The section on typed values and string values has been edited to clarify that an implementation may store either value and derive the other. Also, an example has been added to illustrate the typed value of a union type.
In a validate
expression, the node to be validated is now mapped directly to an Infoset using the mapping defined in the Data Model, rather than being serialized and parsed.
Various minor changes, both editorial and substantive, have been made in response to public comments and working group discussions.