Information Today
Volume 18, Issue 6 — June 2001
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W3C Issues XML Schema as a W3C Recommendation

The World Wide Web Consortium (W3C) has announced that it has issued XML Schema as a W3C Recommendation. XML Schemas define shared markup vocabularies—the structure of XML documents that 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, which is in favor of supporting its adoption by academic, industry, and research communities.

With over 2 years of development and testing through implementation, XML Schema provides an essential piece for XML to reach its full potential, according to the announcement. "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 for 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 that use multiple namespaces defined by different schemas, according to the announcement.

The XML Schema specification consists of three parts. The first 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 that explains what schemas are, how they differ from document type definitions, and how someone builds a schema.

According to the announcement, XML Schema introduces new levels of flexibility that may accelerate the adoption of XML for significant industrial use. For example, an 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 users to develop XML Schemas that best suit their needs without building an entirely new vocabulary from scratch.

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

The XML Schema has broad support among information technology leaders in research and industry such as Arbortext, Inc.; Hewlett-Packard Co.; IBM; Informix; Intel; Lotus Development Corp.; Microsoft Corp.; Oracle Corp.; Sun Microsystems; and Xerox. Many are committed to current and future product support for the XML Schema Recommendation. W3C invites developers to send in sample schemas for a test suite library that will be reviewed and managed by the W3C XML Schema Working Group.

The W3C is an international industry consortium jointly run by the MIT Laboratory for Computer Science (MIT LCS) in the U.S., the National Institute for Research in Computer Science and Control (INRIA) in France, and Keio University in Japan. Services provided by the consortium include a repository of information about the World Wide Web for developers and users and various prototype and sample applications to demonstrate the use of new technology. To date, over 510 organizations are members of the consortium.

Source: World Wide Web Consortium, 617/253-5884;

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