3. XHTML Schema Modules

This chapter is normative.

3.1. XHTML Abstract Modules

The DTD modularization framework specification speaks at length on the subject of abstract modules. In brief, an "abstract" module is simply a set of objects, in this case objects within an ordered hierarchy of content objects, which encapsulates all of the features of the objects and assembles them into a coherent set. This set of objects and their properties is independent of its machine representation, and so is the same whether written in DTD module form, as a Schema module, or as a Java class.

The abstract modules described in XHTML-MOD are composed in a functional manner, and each "abstract module" contains data structures that are generally functionally similar. (There is no requirement that modules be created along functional lines; any other method that suits the author's purpose may be used instead.)

The framework described here makes use of the same abstract modules as in XHTML-MOD with few exceptions. In the case of the schema module representation, the relationship between the "abstract" modules and the schema modules is quite close. In each case there is a one-to-one relationship between the abstract and concrete modules (with one exception for the changes to the legacy module) and they share essentially the same names and data structures.

3.2. XHTML Schema Modules

3.2.1. Required Modules

These modules must be included in any document that uses the XHTML namespace. Each section below describes the purpose of the module and its contents.

None of the modules defined here should be modified by developers; instead use <redefine> or a substitution group.

3.2.1.1. Framework Modules

This is a module container for XHTML language support modules.

3.2.1.1.1. Notations

3.2.1.1.2. Data types

3.2.1.1.3. Common Attributes

3.2.1.1.4. Common Content Models

3.2.1.1.5. Character Entities

The character entities module includes three DTD modules, each referencing one of the required entity sets in XHTML: ISO Latin-1, Symbols, and Special characters.

Character entities are not fully supported in XML Schema, as described in Section 2.1.

3.2.1.2. Core Element Modules

These are the core element definitions for the required modules.

3.2.1.2.1. Text Modules

Block Phrasal

Block Structural

Inline Phrasal

  Inline Structural

3.2.1.2.2. Hypertext

3.2.1.2.3. Lists

3.2.1.2.4. Structural

3.2.2. Optional Modules

These modules are (clearly) optional; they may be removed or combined arbitrarily (except for dependencies). Developers should not modify the contents of these files as they part of the XHTML definition. Instead, extension in the optional modules should be confined to redefinitions and derivations.

3.2.2.1. Edit

3.2.2.2. Bdo

3.2.2.3. Presentational

3.2.2.3.1. Inline Presentational

3.2.2.3.2. Block Presentational

3.2.2.4. Link

3.2.2.5. Meta

3.2.2.6. Base

3.2.2.7. Scripting

3.2.2.8. Style

3.2.2.9. Image

3.2.2.10. Client-side Image Maps

3.2.2.11. Server-side Image Maps

3.2.2.12. Param

3.2.2.13. Applet

3.2.2.14. Object

3.2.2.15. Tables

3.2.2.16. Forms

3.2.2.17. Nameident

3.2.2.18. Legacy

This module has been reorganized to conform to the framework conventions used here. It has been divided here into two separate modules. The "misc" module contains everything in the DTD legacy model except frames. Frames are now in a separate module called framedefs. This allows the developer to easily separate the legacy features if desired.

3.2.2.18.1. Misc

3.2.2.18.2. Framedefs

Frames

Target

Iframe

3.2.2.19. Basic Forms

3.2.2.20. Basic Tables

3.2.2.21. Events

3.2.3. Ruby

Ruby elements denote annotations used in some Asian languages [RUBY].

The Ruby module has been moved into the optional element definitions module. Note that it is normatively required in XHTML 1.1

3.2.4. XHTML Hub Document   (Non-normative)

This is an example base schema document that includes all the other modules to create the complete schema.

3.2.4.1. XHTML 1.1

The hub document included here intends to approximate XHTML 1.1 subject to the requirements given in Section 1.4. This schema should be fully equivalent to the DTD version except for schema-specific additions and changes. This hub document is non-normative and provided only as an example.

3.3. Validity and Conformance

The purpose of any language definition, regardless of its basis on DTDs, XML Schema, or some other representation, is the same: to determine if a specific document instance conforms to the language definition. In XML Schema terms, this means that documents can be validated using the schema. The validation process attempts to determine the document's structural integrity, and the behavior of any XML processor in cases of validation errors is well-defined in the XML 1.0 specification. Therefore the real test of any modularization system for XHTML is whether the resulting schema can be used to determine if any particular XHTML document instance is valid.

This document does not attempt to define conformance beyond the ability to validate the structural integrity of documents. In particular it does not attempt to describe any level of user-agent conformance, as this is not a modularization issue, but an issue for the specification of the language semantics. Conformance to the XML Schema-based modularization framework is strictly defined in terms of document validation. Further levels of conformance are described in the published language specifications themselves.

3.3.1. XHTML Conformance

Schemas defining language variants within the XHTML namespace may be considered to be conformant if they:

• Conform to the existing published language definition for that language variant
• Include all of the modules that are required in this document
• Retain the semantic components of the required elements intact including but not limited to elements, attributes, and attribute values
• Properly identify external elements and attributes with the appropriate XML namespace
• Any combination of the XHTML Schema modules provided that complies with these rules can be considered to be a conformant language variant in the XHTML namespace.

3.3.2. Schema Modularization Conformance

An XML Schema or set of Schema modules can be considered to be conformant to this schema modularization framework if they follow the schema modularization framework conventions described in Section 2.2.

3.3.3. The XHTML Family of Documents

The XHTML Family of Documents is defined as the set of language variants that use the XHTML namespace as the namespace of the root element, which must be <html>.

In order to be a conformant member of the XHTML Family of Documents, an XML Schema or set of schema modules must:

• Define <html> as its root element, and use the XHTML namespace as the root element's namespace.
• Conform to the XHTML Conformance and Schema Modularization Conformance sections of this document.

This class of document definitions includes both XHTML language variants and compound document types using external modules.