An ISO Committee Draft for Document Schema Definition Languages (DSDL) -- Part 4: Selection of Validation Candidates has been released by members of the ISO DSDL Project. The DSDL standard is being published as a multi-part specification; it "brings together multiple schema languages into a single framework that allows them to work together." The DSDL Validation Candidate Selection Language (VCSL) is an "XML-based language for controlling selection of validation candidates. DSDL allows specific parts of an XML document to be extracted and then validated; different schema languages and validators may be applied to different candidates. Descriptions in DSDL VCSL may be independent XML documents or they may be embedded in other XML documents. Specifically, when a DSDL framework is represtented by an XML document, it may reference to or contain descriptions in DSDL VCSL." DSDL Part 4 has been produced under the direction of project editor MURATA Makoto through within ISO/IEC JTC 1/SC34/WG1 (Information Technology -- Document Description and Processing Languages -- Information Description).

Bibliographic information: Document Schema Definition Languages (DSDL) -- Part 4: Selection of Validation Candidates. Committee Draft ISO/IEC 19757-4. Reference: ISO/IEC JTC 1/SC34 N363 (Draft). Project Editor: MURATA Makoto (Japan). From ISO/IEC JTC 1/SC34/WG1: Information Technology -- Document Description and Processing Languages -- Information Description. December 11, 2002.

Overview

Different parts of an XML document may require different schema languages. Typical examples are narrative documents containing metadata. Narrative documents may be written in DocBook, TEI, or XHTML. General-purpose schema languages such as RELAX NG and DTD are appropriate for describing schemas for such narrative documents. On the other hand, embedded metadata may be topic maps or RDF metadata. Special-purpose schema languages such as Topic Map Constraint Language or RDF Schema are appropriate for describing schemas for such metadatda.

DSDL brings together multiple schema languages into a single framework that allows them to work together. In particular, this part of DSDL allows selection of validation candidates. That is, DSDL allows specific parts of an XML document to be extracted and then validated. Different schema languages and validators may be applied to different candidates.

[Part 4 of the DSDL] International Standard introduces an XML-based language for controlling selection of validation candidates. This language is called DSDL VCSL (DSDL Validation Candidate Selection Language). RELAX NG (Part 2), Schematron (Part 3), Path-based integrity constraint language (Part 6), and even non-DSDL schema languages (e.g., RDF Schema and Topic Map Constraing Language) may be used to validate extracted validation candidates. However, it is outside the scope of this part to specify which schema and schema language is used for extracted validation candidates. Descriptions in DSDL VCSL may be independent XML documents or they may be embedded in other XML documents. Specifically, when a DSDL framework is represtented by an XML document, it may reference to or contain descriptions in DSDL VCSL... [From the Introduction and Scope Statement]

Related news: Modular Namespaces (MNS)

James Clark recently announced a Modular Namespaces (MNS) language which supports validation from multiple independent namespaces. "The XML Namespaces Recommendation allows an XML document to be composed of elements and attributes from multiple independent namespaces. Each of these namespaces may have its own schema. The problem then arises of how the schemas can be composed in order to allow validation of the complete document. In RELAX Namespace, Murata Makoto pioneered the idea of dividing the document into islands, with each island containing a single namespace, and validating each island separately against the schema for its namespace. RELAX Namespace formed the basis for the recently published Committee Draft of Document Schema Definition Languages (DSDL) -- Part 4: Selection of Validation Candidates. [This] language named Modular Namespaces (MNS) is an evolution of the ideas in RELAX Namespace and DSDL Part 4. RELAX Namespace was designed to work well with RELAX Core. RELAX Core cannot deal with documents that use multiple namespaces, nor does it provide any namespace-based wildcards. These limitations of RELAX Core are reflected in the design of RELAX Namespace. MNS is designed to be able to take advantage of more recent schema languages, such as RELAX NG, that are not limited in this way... There's a new release of Jing that includes a sample implementation. MNS is designed to be useful when: (1) you have an instance that uses elements and attributes from multiple namespaces; (2) you have one or more schemas (not necessarily all in the same schema language) each of which deals with one or more of these namespaces; (3) you want to use all these schemas to validate the instance..."