OWL 2 Web Ontology Language:
Profiles

W3C Editor's Draft 11 April22 September 2008

This version:

http://www.w3.org/2007/OWL/draft/ED-owl2-profiles-20080411/http://www.w3.org/2007/OWL/draft/ED-owl2-profiles-20080922/

Latest editor's draft:

http://www.w3.org/2007/OWL/draft/owl2-profiles/

Previous version:

http://www.w3.org/2007/OWL/draft/ED-owl2-profiles-20080408/http://www.w3.org/2007/OWL/draft/ED-owl2-profiles-20080411/ (color-coded diff)

Authors:

Bernardo Cuenca Grau, Oxford University

Boris Motik, Oxford University

Zhe Wu, Oracle

Achille Fokoue, IBM

Carsten Lutz, Dresden University of Technology

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Copyright © 2008 W3C^® (MIT, ERCIM, Keio), All Rights Reserved. W3C liability, trademark and document use rules apply.

Abstract

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May Be Superseded

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Set of Documents

This document is being published as one of a set of 68 documents:

1. Structural Specification and Functional-Style Syntax
2. Model-Theoretic Semantics
3. RDF-Based Semantics
4. Mapping to RDF Graphs
5. XML Serialization
6. Profiles (this document)
7. Primer Compatibility with OWL 1 The OWL Working Group intends to make OWL 2 beConformance and Test Cases
8. A superset of OWL 1, exceptDatatype for some small bug fixes and changes to the formal semantics of annotations. This means that OWL 2 will be backward compatible, and creators of OWL 1 documents need only move to OWL 2 when they want to make use of OWL 2 features. More details and advice concerning migration from OWL 1 to OWL 2 will be in future drafts.Internationalized Text

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The EL++choice of profile enables polynomial time algorithms forwill depend on the reasoning tasks consistency, classification,structure of the ontologies used in the application and instance checking. Dedicatedon the reasoning algorithms for this profile are available and have been demonstratedtasks to be implementable in a highly scalable way. In the DL-Lite profile,performed, for example (ontology) consistency, (class) satisfiability, (class) subsumption, classification and conjunctive query answeringanswering. Precise definitions of these tasks can be implemented using conventional relational database systems (after rewriting the query).found in particular, this requires that conjunctive query answeringSection 5.

• OWL 2 EL is particularly useful in LogSpace regarding data complexity. As in EL++, there are polynomial time algorithmsapplications employing ontologies that contain very large numbers of properties and/or classes: it captures the expressive power used by many such ontologies and is the maximal subset of OWL 2 for which the basic reasoning problems (i.e., consistency, satisfiability, subsumption, classification, and instance checking. The OWL-R profile enableschecking) can be performed in time that is polynomial with respect to the implementationsize of the ontology. Dedicated reasoning algorithms by forward chaining rules appliedfor this profile are available and have been demonstrated to triples of the RDF serialization. In particular, such rule approaches canbe used to compute consistency, classification, andimplementable in a highly scalable way.
• OWL 2 QL is aimed at applications that use very large volumes of instance checkingdata, and where query answering is the most important reasoning task. In polynomial time.OWL 2 QL, conjunctive query answering in OWL-Rcan be implemented by extending a standardusing conventional relational database system with rules. OWL-R comes in two varieties, OWL-R DLsystems, and OWL-R Full. The profiles EL++, DL-Lite,can directly access data stored in such systems. Using this technique, sound and OWL-R DL are defined by placing restrictions oncomplete query answering can be performed in LOGSPACE with respect to the syntaxsize of the data (assertions). As in OWL 2 DL. In contrast, OWL-R FullEL, there are polynomial time algorithms for consistency, subsumption and classification reasoning. The expressive power of the profile is defined by placing restrictions onnecessarily quite limited, although it does include most of the semanticsmain features of conceptual models such as UML class diagrams and ER diagrams.
• OWL 2 Full. Editor's Note: The working group intends to provide more guidance for users about how to select a profile well suited for their situation.RL is aimed at applications that require scalable reasoning without sacrificing too much expressive power. It is not yet determined whetherdesigned to accommodate both OWL 2 applications that guidance will be here or in the Primer. Syntactic restrictionscan be specified by modifyingtrade the grammarfull expressivity of the language for efficiency, and RDF(S) applications that need some added expressivity. OWL 2 RL reasoning systems can be implemented using relatively simple technology, in particular, rule-based reasoning engines — conjunctive query answering can be implemented by extending a standard relational database system with rules. Such rule-based approaches can be used to perform consistency, satisfiability, subsumption, classification, and instance checking in time that is polynomial with respect to the size of the ontology.

OWL 2 profiles are defined by placing restrictions on the OWL 2 syntax. Syntactic restrictions can be specified by modifying the grammar of the functional-style syntax [OWL 2 Specification], and (possibly) giving additional non-structuralglobal restrictions. In this document, the modified grammars are specified in two ways. In each section defining a profile,profile definition, only the difference with respect to the full grammar is given; that is, only the productions that differ from [OWL 2 Specification] are presented and the productions that are the same as in [OWL 2 Specification] are not repeated. In order to make this document self-contained, the full grammar for each of the fragmentsprofiles is given in the Appendix.

The reasoning tasks mentioned in the description of the profiles are defined as follows. consistency: given an ontology, decide whether it is contradictory (i.e., has any models); classification: given an ontology, compute the subclass relation between all its classes; instance checking: given an individual a and a class C in an ontology, decide whether a is an instance of C; conjunctive query answering: given an ontology O and a conjunctive query q, return all tuples of individuals in O that match q.Apart from the ones specified here, there are many other possible profiles of OWL 2.2 — there are, for example, the OWL Lite versiona whole family of profiles that extend OWL 12 QL. Although we don't specifically document OWL lite [OWL 1 Reference] in this document, all OWL Lite ontologies are OWL 2 DL ontologies and so OWL Lite can be viewed as a profile of OWL 2. Since its computational properties have turned out to be less good than suspected when the OWL 1 recommendation was passed (e.g., satisifiability and subsumption are ExpTime-complete), OWL 1 Lite is not treated explicitly in this document.OWL 1 DL can also be viewed as a profile of OWL 2.

Editor's Note: See ISSUE-108The Working Group hasitalicized keywords MUST, MUST NOT yet comitted itself to the names, SHOULD, SHOULD NOT, and MAY specify certain aspects of different profiles.the names used in this document are likely to change in future. Editor's Note: At the second F2F meeting, the Working Group has decided to simplify the vocabularynormative behavior of OWL ontologies. In future versions of this specification, the terminals of the functional-style grammar2 tools, and the RDF vocabulary will be significantly smaller.are interpreted as specified in RFC 2119 [RFC 2119].

The EL++OWL 2 EL profile [EL++,EL++ Update] is designed as a maximal subset of OWL 2 DLthat

• captures the expressive power used by many large-scale ontologies and
• for which the following reasoning problems can be decided in polynomial time: satisfiability, subsumption, classification, and instance checking.

A main design principle of EL++OWL 2 EL is to focus on the class constructors ObjectIntersectionOf and ObjectSomeValuesFrom, but to provide ObjectAllValuesFrom only in the form of range restrictions. Many biomedical ontologies, such as SNOMED CT, fall within this profile.

The productions forclass constructorsexpressions are as defined in the same way as in OWL 2 [OWL 2 Specification], with the exception of the objectOneOf class expression, which in OWL 2 EL admits only a single individual:individual.

The class axioms of EL++OWL 2 EL are the same as in fullOWL 2, exceptwith the exception that DisjointUnion is not allowed.disallowed. Different class axioms are defined in the same way as in [OWL 2 Specification], with the difference that they use the new definition of ClassExpression.

OWL 2 EL supports the productions for all supported kinds class axiomsfollowing object property axioms, which are defined in the same way as in the [OWL 2 Specification], with the difference that they use the new description production. We refer to that document for details. EL++ supports the following object property axioms.definition of ObjectPropertyExpression.

The productions for all supported kinds of object property axioms are as in the [OWL 2 Specification ]. EL++ disallows DisjointObjectProperties , IrreflexiveObjectProperty , InverseObjectProperties , FunctionalObjectProperty , SymmetricObjectProperty , and AsymmetricObjectProperty axioms. Regarding data property axioms, EL++EL provides the same facilitiesaxioms about data properties as OWL 2, except2 apart from DisjointDataProperty. Therefore, data propertyThese axioms in EL++are defined in the same way as follows.in [OWL 2 Specification].

Again,The productions for all supported kinds of property axioms are asassertions in the [OWL 2 Specification ]. The facts in EL++EL, as well as all other axioms, are the same as in OWL 2, with the diffencedifference that descriptions andclass object property expressions are restricted as specified previously. Finally, the axioms of EL++ are the same asdefined in OWL 2, withthe difference that each axiom type is restricted as specified previously.previous sections.

OWL 2 EL extends the global restrictions described inon axioms from Section 1011 of the structural specification [OWL 2 Specification ]. To obtain polytime reasoning problems, one] with an additional restrictioncondition. In order to define this condition, the following notion is imposed.used.

Let CE be a class expression. We say that Ax imposes a range restriction to CE on an object property PEOP₁ if itobject properties OP_i, 2 ≤ i ≤ k, exist such that Ax contains axioms SubObjectPropertyOf(PEall of the following axioms:

• SubPropertyOf( OP₁ PEOP₂ ),...,SubObjectPropertyOf(PE)
• ...
• SubPropertyOf( OP_k-1 PEOP_k )
• ObjectPropertyRange(PEPropertyRange( OP_k CE) We require thatCE )

The axiom closure Ax of an OWL 2 EL ontology MUST obey the restrictions described in Section 11 of the structural specification [OWL 2 Specification] and, in addition, if

• Ax contains SubObjectPropertyOf(SubObjectPropertyChain(PESubPropertyOf( PropertyChain( OP₁ ... PEOP_n ) PE)OP ) and
• Ax imposes a range restriction to some class expression CE on PEOP

then Ax imposesMUST impose a range restriction to CE on PEOP_n.

Remarks: (1) TheThis additional restriction is vacuously true if the SubObjectPropertyOffor each SubPropertyOf axiom in which in the first item is a role inclusion statement -- that is, if itof the previous definition does not contain SubObjectPropertyChain . (2)a property chain. Range restrictions on reflexive and transitive roles are generally allowed, unless they are used in axioms following thethat are explicitly forbidden pattern above.using the previous definition.

OWL 2 QL is based on the DL-Lite family of description logics. Several variants of DL-Lite have been described in the literature. The variant presented hereliterature [DL-Lite]. OWL 2 QL is calledbased on the DL-Lite_R since it allows for property inclusion axioms; it therefore contains— an expressive DL containing the intersection betweenof RDFS and OWL 2 DL. Other2. DL-Lite_R does not require the unique name assumption (UNA), since making this assumption would have no impact on the semantic consequences of a DL-Lite_R ontology. More expressive variants trade property inclusion axiomsof DL-Lite, such as DL-Lite_A, extend DL-Lite_R with functional properties, and these can also be extended with keys; however, for functionalityquery answering to remain in LOGSPACE, these extensions require UNA and inverse-functionalityneed to impose certain global restriction on the interaction between properties used in different types of object properties. Note thataxiom. Basing OWL 2 QL on DL-Lite_R avoids practical problems involved in the profile presented here is asymmetric: itexplicit axiomatization of UNA. Other variants of DL-Lite can also be supported on top of OWL 2 QL, but may require additional restrictions on the structure of ontologies [DL-Lite].

OWL 2 QL is defined not only in terms of the set of supported constructs, but it also restricts the places in which these constructs can be used. Editor's Note: Please note that Data Propertiesare not yet incorporated into DL-Lite in this draft, pending consultation with some DL-Lite experts . Editor's Note: See ISSUE-80 (DL-Lite) This document currently contains the DL-lite R version of DL-lite. In future versions of this document, however, this language is likelyallowed to be extended with additional constructs that preserve its computational properties, such as Data Properties and suitably restricted Functional Properties.occur.

The productions for DL-LiteOWL 2 QL are defined in the following sections. The expressive power of OWL 2 QL is such that the global restricitonsrestriction on axioms defined in the structural specificationSection 11 of [OWL 2 Specification] are not enforcedvacuously satisfied in DL-Lite.every DL-lite ontology.

The class axioms of OWL 2 QL are the same as in OWL 2, with the exception that DisjointUnion is disallowed. Different OWL 2 DL. 3.2.4 Axioms DL-Lite axioms are defined to exclude membership assertions on data properties. axiom  := classAxiom | objectPropertyAxiom | fact | declaration | entityAnnotation Furthermore, DL-Lite redefines allclass axioms from the functional-style syntaxstructural specification [OWL 2 Specification] that refer to the description production. In particular, it restricts various class axiomsClassExpression production, however, are redefined and restricted them to appropriate forms of classes, and it disallows DisjointUnion . The production for axioms about classes in DL-Lite are defined as follows.class expressions.

DL-LiteOWL 2 QL disallows the use of property chains in property inclusion axioms (simpleaxioms; however, simple property inclusions are just like insupported. Furthermore, OWL 2), it2 QL disallows the use of functional, transitive, asymmetric, reflexive and irreflexive object properties, and it redefines theobject property domain and range axioms to use the newappropriate class productions.expressions.

Editor's Note: I assume that negativeObjectPropertyAssertion is not supported by DL-Lite DL-LiteOWL 2 QL disallows axioms aboutthe functional data propertiesproperty axioms, and it redefines the object property domain axioms to use the appropriate class expressions.

OWL 2 QL disallows negative object property assertion.assertions and equality axioms. Furthermore, class membershipassertions in DL-Lite are restricted toOWL 2 QL can involve only atomic classes. Equality and inequality axioms and property membershipassertions are the same as in OWL 2.

Finally, the axioms in OWL 2 that allows for scalable reasoning using rule-based technologies.QL are the profile has been designed sosame as to avoid the need to inferthose in OWL 2, with the existence of individualsexception that keys are not explicitly present inallowed.

The knowledge base. This design goal enables a straightforward translation of OWL’s semantic conditions into rules, on which most rule-basedOWL 2 RL profile is aimed at applications that require scalable reasoning engines terminate in a finite amount of time. Another design goal for OWL-Rwithout sacrificing too much expressive power. It is flexibility. On the one hand, OWL-R candesigned to accommodate both OWL 2 DLapplications that can trade the full expressivity of the language for efficiency; on the other hand, OWL-R can also accommodateefficiency, and RDF(S) applications that need some added expressivity from OWL. For this purpose,OWL 2. This document provides two variants of OWL-R. The first variant of OWL-R, called OWL-R DL,is intended to be usedachieved by defining a syntactic subset of OWL 2 DL users who can trade some expressivity for being ablewhich is amenable to implement reasoningimplementation using rule-based systems. OWL-R DL is defined astechnologies (see Section 4.2), and presenting a syntactic subsetpartial axiomatization of the OWL 2 DL -- that is, it places syntactic restrictions on OWL 2 DL axioms. For example,RDF-Based Semantics in this definition, one cannot declare an OWL class C1 to be a subclass ofthe unionform of two classes C2 and C3.first-order implications that can be used as the definition of OWL-R DL is presented completelybasis for such an implementation (see Section 4.3).

For ontologies satisfying the syntactic constraints described in Section 4.2 ., a suitable rule-based implementation will have desirable computational properties; for example, it can return all and only the second variant OWL-R, called OWL-R Full, is intendedcorrect answers to certain kinds of query (see Section 4.4 and Conformance). Such an implementation can also be used by RDF(S) users who want to augment RDF(S)with additional contructs. OWL-R Full ontologies are thusarbitrary RDF graphsgraphs. In this case, however, these properties no longer hold — in particular, it is no longer possible to guarantee that are interpreted under a weakened version ofall correct answers can be returned.

Unlike OWL-R DL, in OWL-R Full there are no syntactic restrictionsImplementations based on the way language constructspartial axiomatization (presented in Section 4.3) can also be used: anyused with arbitrary RDF graph constitutes a valid OWL-R Full ontology. The semantics of language constructs, however, is weakenedgraphs, but in OWL-R Fullthis case it is no longer possible to mimicprovide the usage patterns of OWL-R DL.above mentioned computational guarantees. Such implementations will, however, still produce only correct entailments (see Conformance).

The productions for example, inOWL 2 Full (or DL), anRL are defined in the following sections. OWL class C12 RL is a subclass of C2 if anddefined not only if the extension of C1 is a subsetin terms of the extensionset of C2. In OWL-R Full, that "if and only if" condition is weakened to "only if."supported constructs, but it also restricts the principles according to which this weakening has been derived are presentedplaces in Section 4.3.1 . An equivalent characterization ofwhich these constructs can be used. The weakened semantics by means of first-order implications is given in Section 4.3.2 . Table 2 lists the language constructs that are supported in OWL-R Full. Table 2. The Constructs Supported in OWL-R Full Equality owl:sameAs owl:differentFrom Property Expressions owl:inverseObjectPropertyExpression Property Axioms rdfs:domain rdfs:range owl:FunctionalProperty owl:InverseFunctionalProperty owl2:ReflexiveProperty owl2:IrreflexiveProperty owl:SymmetricProperty owl2:AsymmetricProperty owl:TransitiveProperty rdfs:subPropertyOf owl2:propertyChain owl:equivalentProperty owl2:propertyDisjointWith owl2:disjointDataProperties owl:inverseOf Class Constructs owl:intersectionOf owl:unionOf owl:someValuesFrom owl:allValuesFrom owl:hasValue owl:maxCardinality 1 Class Axioms rdfs:subClassOf owl:equivalentClass owl:disjointClasses 4.2 OWL-R DL OWL-R DL is a syntactic profile of OWL 2 DL. The profile is defined not only in terms of a set of supported constructs, but it also restricts the places in which these constructs can be used. Itidea is based on Description Logic Programs [DLP] --— a logic obtained by intersecting description logics with rule-based languages.

Property expressions in OWL-R DL, a data range expression is restricted to either a named atomic datatype (the list of datatypes supported by OWL-R DL isOWL 2 RL are identical to the oneproperty expressions in OWL 2 [OWL 2 Semantics ]) or a datatype restriction, specified by applying some facets to limit the value space of an pre-existing datatype. dataRange  := datatypeURI | datatypeRestrictionSpecification].

OWL-ROWL 2 RL redefines all axioms from the functional-style syntaxof [OWL 2 Specification] that refer to the description production.ClassExpression. In particular, it restricts various class axioms to use the appropriate form of class expressions (i.e.(i.e., one of subClasssubClassExpression, superClasssuperClassExpression, or equivClassequivClassExpression), and it disallows the DisjointUnion axiom.

OWL-ROWL 2 RL axioms about property expression language is very similar toexpressions are as in OWL 2.2, the only difference isbeing that OWL-R restrictsproperty domain and range axioms are restricted to the appropriate form of class expressions as follows:expressions.

OWL vocabulary related2 RL restricts the positive assertions to boolean combinationsa particular type of classes, and sets, the conditions for owl:complementOfit disallows negative property assertions. Equality and owl:oneOf are dropped,inequality between individuals and positive assertions are the condition for owl:unionOf is changed into only-if . The condition for owl:intersectionOf is left unchanged. The table defining the conditions on OWL restrictions is modifiedsame as follows. The condifion for owl:allValuesFrom is changed into CEXT I (x) ⊆ {u ∈ IOT | < u,v > ∈ EXT I (p) implies v ∈ CEXT I (y)in OWL 2.

Keys are redefined in OWL 2 RL to allow for owl:hasValue is let unchanged.correct type of class expression in the conditions for cardinality restrictionsaxiom.

All other axioms in OWL 2 RL are changed such that y must be 1,defined as in OWL 2.

The implicationsrules are given as universally quantified first-order implications over a ternary predicate T. This predicate represents a generalization of RDF triples in which bnodes and literals are allowed in all positions (similar to the partial generalization in pD* [pD*] and to generalized RDF triples;triples in RIF [RIF]); thus, T(s, p, o) represents a generalized RDF triple with the subject s , predicate psubject s, predicate p, and the object o. Variables in the implications are preceded with the question mark. The propositional symbol false is a special symbol denoting contradiction: if it is derived, then the initial RDF graph was inconsistent.

Many conditions contain atoms that match to the list construct of RDF. In order to simplify the presentation of the rules, LIST[h, e₁, and..., e_n] is used as an abbreviation for the object o . Variablesconjunction of triples shown in the implicationsTable 2, where z₂, ..., z_n are preceeded withfresh variables that do not occur anywhere where the question mark.abbreviation is used.

The semantic conditions areaxiomatization is split into several tables for easier navigation. These tables are exhaustive: they specify exactly all the semantic conditions that must hold.Table 13 axiomatizes the semantics of equality. In particular, it defines the equality relation on resources owl:sameAs as being reflexive, symmetric, and transitive, and it axiomatizes the standard replacement properties of equality for it.

Table 24 specifies the semantic conditions on axioms about properties.

Table 35 specifies the semantic conditions on classes.