http://www.w3.org/ -- The World Wide Web Consortium (W3C) has issued XML Schema as a W3C Candidate Recommendation. Advancement of the document to Candidate Recommendation is an invitation to the Web development community at large to make implementations of XML Schema and provide technical feedback.

XML Schema Accelerates the XML Revolution
Simply defined, XML Schemas define shared markup vocabularies and allow machines to carry out rules made by people. They provide a means for defining the structure, content and semantics of XML documents.

"Databases, ERP and EDI systems all know the difference between a date and a string of text, but before today, there was no standard way to teach your XML systems the difference. Now there is," declared Dave Hollander, co-chair of the W3C XML Schema Working Group and CTO of Contivo, Inc. "W3C XML Schemas bring to XML the rich data descriptions that are common to other business systems but were missing from XML. Now, developers of XML ecommerce systems can test XML Schema's ability to define XML applications that are far more sophisticated in how they describe, create, manage and validate the information that fuels B2B ecommerce."

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.

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.

XML Schema Introduces Flexibility, Data Fidelity for Users
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 is Ready for Implementors
Candidate Recommendation is W3C's public call for implementation, an explicit invitation for W3C members and the developer community at large to review the XML Schema specification and build their own XML Schemas. This period of implementations and reporting allows the editors to learn how developers outside of the Working Group might use them, and where there may be ambiguities for implementors. Public testing and implementation contribute to a more robust XML Schema, and to more widespread use.

XML Schema Has Broad Support
The working group roster reads as a who's who of information technology leaders in research and industry. The members include: Academia Sinica; ArborText, Inc; Bootstrap Alliance and LSU; Calico Commerce; Commerce One; Defense Information Systems Agency (DISA); DevelopMentor; Distributed Systems Technology Centre (DSTC Pty Ltd); Graphic Communications Association; Health Level Seven; Hewlett Packard Company; IBM; Informix; Intel; Lawrence Berkeley National Laboratory; Lexica LLC; Lotus Development Corporation; Microsoft Corporation; Microstar; MITRE; NCR; Oracle Corp.; Progress Software; SAP AG; Software AG; Sun Microsystems; TIBCO Software; University of Edinburgh; webMethods, Inc; Xerox; and XMLSolutions.

Many are committed to current and future product support for XML Schema as it progresses to W3C Recommendation.