Foreword

clas•sic (adjective)
judged over a period of time to be important and of the highest quality:

a classic novel
a classic car

Neither this definition, nor any of the leading dictionary definitions, has a usage example anything like:

a classic work on high-tech software

After all, it is a rare book on software that even survives long enough to be “judged over a period of time.”

Nevertheless, Definitive XML Schema satisfies every definition of “classic.” It is one of the elite few software books that have been in print continuously for over ten years, and an essential trustworthy guide for tens of thousands of readers.

This Second Edition continues to be an essential and trustworthy classic:

Essential because in the last ten years XML has become the accepted standard for data interchange, and XML Schema 1.0 is largely responsible. Now version 1.1 has extended the ability to specify and validate document data, to a degree previously possible only for databases. These updates are covered in this book by extensive revisions—the most significant 250 of which are flagged in the text and table of contents. Hundreds more unflagged revisions reflect W3C corrections of XML Schema errata, and ten years of evolving “best practices.”

Trustworthy because it is both authoritative and accurate.

• The author(ity), Priscilla Walmsley, is a noted consultant who has been using XML Schema ever since she helped develop it as a member of the W3C XML Schema Group. She personally devised many of the current “best practices” described in this book. Priscilla is the Editor of the W3C XML Schema Primer, Second Edition.

• Accuracy was preserved by using the same XML-based production system that was used in 2002, operated by the same team of XML experts who read and thoroughly understood the book. Priscilla’s original XML source (in which she had personally tagged the version 1.1 revisions) was used throughout production. Dmitry Kirsanov copy-edited and proofed it, while Alina Kirsanova prepared the index, coded the XSL transformations, and generated the camera-ready PDFs.

The result, as you will see, retains the structure, clarity, patient explanations, validated examples (over 450!), and well-reasoned advice that critics praised in the 2002 edition—but now they are ten years more up-to-date.

And after you’ve read Definitive XML Schema, Second Edition, it won’t take another ten years for you, too, to judge it a classic.

Charles F. Goldfarb
Belmont, CA
August 2012