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> -----Original Message----- > From: Elliotte Rusty Harold [mailto:elharo@m...] > Sent: Friday, December 07, 2001 7:24 PM > To: xml-dev@l... > Subject: RE: Attribute Order > > > So far Schematron's the most powerful language, but it still hasn't > reached Turing completeness. Using actual program code lets your > schemas verify criteria of types one and two. Type three is still an > area of active research. But existing schema languages seem mostly > stuck at Type 0. Sorry, I'm not familiar with this categorization ... what "criteria of types" being referred to here? Anyway, I completely agree -- it's perfectly reasonable for schema designers to specify constraints that can't be expressed in an existing XML schema language. We went around on this a couple of months ago, and as I recall we concluded: - schemas are certainly useful to define "contracts" constraining the markup that a receiver is expected to understand; - schema validators or validating parsers may are likely to be very useful in debugging or auditing software to ensure that the contract is being adhered to; - XML-level validation may, in some (limited?) circumstances, suffice as the "business logic" to ensure that an XML document or message should be accepted by some receiving process. - XML-level validation is more likely to be useful as a cost-effective way of doing a coarse-grained screening out of blatantly unacceptable documents or messages so that program code can check the constraints that can't be expressed in a schema language. Whether it makes sense to do both the schema validation and the programmatic validation is something that individual designers must determine for their own environment. - [this is more my personal understanding than a consensus of the list] Most "real world, real-time" XML document/message validation today involves program code or human intelligence rather than XML DTD or schema validation.
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