World Wide Web Consortium Issues Xml Schema As A W3c Recommendation - Technology Information

EDP Weekly's IT Monitor, May 21, 2001

The World Wide Web Consortium (W3C) issues XML Schema as a W3C Recommendation. XML Schemas define shared markup vocabularies, the structure of XML documents which use those vocabularies, and provide hooks to associate semantics with them.

A W3C Recommendation indicates that a specification is stable, contributes to Web interoperability, and has been reviewed by the W3C Membership, who are in favor of supporting its adoption by academic, industry, and research communities.

With over two years of development and testing through implementation, XML Schema provides an essential piece for XML to reach its full potential.

"XML Schema makes good on the promises of extensibility and power at the heart of XML," said Tim Berners-Lee, W3C Director. "In conjunction with XML Namespaces, XML Schema is the language for building XML applications."

By bringing datatypes to XML, XML Schema increases XML's power and utility to the developers of electronic commerce systems, database authors and anyone interested in using and manipulating large volumes of data on the Web. By providing better integration with XML Namespaces, it makes it easier than it has ever been to define the elements and attributes in a namespace, and to validate documents, which use multiple namespaces defined by different schemas.

The XML Schema specification consists of three parts. One part defines a set of simple datatypes, which can be associated with XML element types and attributes; this allows XML software to do a better job of managing dates, numbers, and other special forms of information. The second part of the specification proposes methods for describing the structure and constraining the contents of XML documents, and defines the rules governing schema-validation of documents. The third part is a primer, which explains what schemas are, how they differ from DTDs, and how someone builds a schema.

XML Schema introduces new levels of flexibility that may accelerate the adoption of XML for significant industrial use. For example, a schema author can build a schema that borrows from a previous schema, but overrides it where new unique features are needed. This principle, called inheritance, is similar to the behavior of Cascading Style Sheets, and allows the user to develop XML Schemas that best suit their needs, without buidling an entirely new vocabulary from scratch.

XML Schema allows the author to determine which parts of a document may be validated, or identify parts of a document where a schema may apply. XML Schema also provides a way for users of ecommerce systems to choose which XML Schema they use to validate elements in a given namespace, thus providing better assurance in ecommerce transactions and greater security against unauthorized changes to validation rules.

Further, as XML Schema are XML documents themselves, they may be managed by XML authoring tools, or through XSLT.

XML Schema Tools Include Validator and Test Suite Collection W3C, with the University of Edinburgh has co-developed XSV, the XML Schema Validator. The validator has been revised at each stage of XML Schema development and now provides validation against the XML Schema Recommendation. In addition, W3C invites developers to send in sample schemas for a test suite library, to be reviewed and managed by the W3C XML Schema Working Group.