|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
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; http://www.w3.org.