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"RELAX NG": A Simpler Schema Language for XML

January 12, 2004

Sebastopol, CA--The beauty of XML is that it is extensible, even to the point that developers can invent new elements and attributes as they write XML documents. Then, however, they need to define their changes so applications will be able to make sense of them. This is where XML schema languages come into play. In his new book, RELAX NG (O'Reilly, US $29.95), author Eric van der Vlist introduces the Regular Language Description for XML Core--New Generation, or RELAX NG (pronounced "relaxing"), an alternative to other schema languages that's quickly gaining momentum. Designed to solve a variety of common problems raised in the creation and sharing of XML vocabularies, RELAX NG is less complex than the W3C's XML Schema Recommendation and much more powerful and flexible than DTDs.

"XML schema languages are a nice idea as long as they don't become so complicated that XML vocabularies built using them are difficult to extend," says van der Vlist. "Unfortunately, that's what was starting to happen before RELAX NG appeared. W3C XML Schema, the dominant XML schema language, is so complex and incorporates ideas from so many conflicting fields that it is difficult to learn, difficult to extend--yet its expressive power is still too limited to describe all the possibilities offered by XML!" Although many applications will to use this mammoth language, van der Vlist adds, many people need the lighter-weight, simpler alternative found in RELAX NG.

Van der Vlist asserts that RELAX NG is easier, more reliable, and safer to use than W3C XML Schema for two primary reasons: RELAX NG has a sound mathematical grounding and focuses on doing a single thing perfectly well--validating the structure of XML documents.

In "RELAX NG," developers are introduced to this unique language and will learn a no-nonsense method for creating XML schemas. This book offers a clear-cut explanation of RELAX NG that enables intermediate and advanced XML developers to focus on XML document structures and content rather than battle the intricacies of yet another convoluted standard.

The book explores this new schema vocabulary from its clean foundations through best practices to integration with other data-description approaches. "RELAX NG" explains both the XML syntax and the compact syntax in depth, showing how to use every pattern in both syntaxes with clear, straightforward examples. The book also explores:

  • How to create W3C XML Schemas or DTDs using RELAX NG
  • Using W3C XML Schemas datatypes and their facets with RELAX NG
  • A variety of schema styles, including their advantages and disadvantages
  • Rules for mixing patterns and the intricacies of the interleave pattern
  • Different approaches to creating modular schemas
  • Generating RELAX NG schemas from other formats
  • Supporting literate programming approaches with RELAX NG
  • Working with XML namespaces in RELAX NG
  • How the W3C uses RELAX NG to address XHTML and SVG modularization
  • Determinism and ambiguity issues in RELAX NG and the W3C XML Schema
  • The OASIS and ISO processes for standardizing RELAX NG
  • RELAX NG offers developers a refreshing approach to describing XML, whether they're defining XML vocabularies for interchange or supporting new metadata in a publishing environment. This book provides a complete guide to this exciting new technology, from how to get started to how best to apply it to many different kinds of XML problems.

    Additional Resources:

    Eric van der Vlist
    ISBN 0-596-00421-4, 506 pages, $29.95 US, $43.95 CA
    1-800-998-9938; 1-707-827-7000

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