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OSCON.

Tutorial

XML Schema Languages
Eric van der Vlist, CEO, Dyomedea

Track: XML
Date: Tuesday, July 27
Time: 8:45am - 12:15pm
Location: Salon E

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Even though a schema language isn't necessary to write an XML document, modeling the structure of XML documents through a schema may help to automate a wide range of tasks such as validation, generation of treatments, or input forms.

van der Vlist’s tutorial presents and compares the main schema languages that are available today to help developers choose the language that best fits their needs, and teaches them how to write Schematron, XSLT, W3C XML Schema, and RELAX NG schemas.

Content includes:

* Rule based schema languages (XSLT and Schematron)
* RELAX NG
* W3C XML Schema

When asked how he became involved with this project, van der Vlist replied, "O'Reilly is definitely solely responsible for my involvement in XML schema languages!

"Back in 2000, when W3C XML Schema wasn't a recommendation yet, I sent to Edd Dumbill a proposal to write an introduction to W3C XML Schema and he accepted it. This introduction has been updated in 2001 and is still available.

"I have learned a lot writing this introduction that required a thorough reading of the specification and its success (it has been amongst the XML.com top pages for a long time) is probably one of the reasons why O'Reilly asked me to write their XML Schema book.

"And the frustrations caused by the complexity and limitations of W3C XML Schema have been my motivations to look for simpler alternatives such as Schematron and RELAX NG, become a member of the ISO DSDL working group and even propose Examplotron, my own schema language!"

Is his tutorial controversial in any way? "Yes, it's very controversial, anything related to the choice between XML schema languages is controversial!

"Many people think that because XML is a W3C recommendation, when you start using XML, you have to buy the whole pile of W3C recommendations and use all of them. That's totally false, these recommendations have been written to be modular and to some attempt, you can just use the ones you like or need.

"And that's terribly important because their level of fit to your needs is very varying, and to put it more bluntly, some of them are technical failures.

"In the domain of XML schema languages, W3C XML Schema which is unfortunately the dominant language is both overly complex and has a limited expressive power and other alternatives such as RELAX NG and Schematron have been proposed and are widely used. RELAX NG is now an ISO DSDL standard and the competition between W3C XML Schema and ISO RELAX NG is very controversial.

"You'll find many W3C XML Schema tutorials around and some few RELAX NG or Schematron tutorial, but as far as I know, this tutorial is the only tutorial that provides an extensive and as objective as possible introduction to XML schema languages at large covering Schematron, RELAX NG, and W3C XML Schema.

"For many attendees, this tutorial is like a door opening to a world of applications that is new to them.

"They get a better understanding of why validating XML documents is crucial, hints of how they can choose the schema language(s) which is/are the best fit(s) for their needs and they are able to start writing simple schemas, find their way in books or tutorials on the subject and avoid some of the common minefields."



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