XML Schema moves forward

Michael Kay
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The XML Schema (XSD) specification from W3C is a paradox: it is one of the most heavily criticised specifications to come out of the organisation, but at the same time it has been widely adopted and implemented, and it can be said to have met all its design objectives.

For some time the responsible working group has been developing a new version, XSD 1.1, which is starting to get close to the finish line. Many of the difficulties with the specification (such as its immense complexity) will still be there, but some of the criticisms, notably those concerned with the limited functionality of the spec, are met head on with some powerful new features. This talk will give a quick overview of what’s new, while concentrating in particular on the way in which Assertions are likely to change the way in which XSD is used. Assertions, borrowed from Schematron, supplement the ability to define constraints using grammar and datatypes by a general predicate mechanism based on XPath. Already implemented in Saxon, they offer far more than the obvious ability to define boolean constraints: the talk will explain how they can be used as a powerful mechanism for tailoring and specializing schemas for use in different environments within an industry community.

The speaker, Dr Michael Kay, is founder of Saxonica Limited which develops the popular Saxon XSLT, XQuery, and XML Schema engine. He is a member of the W3C working groups for all three languages, and author of XSLT 2.0 Programmer’s Reference, the definitive Wrox guide to the language, recently republished in a fourth edition.