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   Re: [xml-dev] Best Practice - beyond schema

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From: "Paul Spencer" <paul@alphaxml.com>

> Using an "open" language to apply further constraints has different
> benefits. 

Here are five other benefits:
 1) The global schema can be simplified
 2) <redefine> is a feature that some implementors may have left to 
  last to get 100% correct
  3) The Schematron schema lets you state the rules as exceptions to
   the global rules, which makes the relationship very clear
  4) Biting the (very small) bullet, and augmenting the main validator with
  Schematron validation makes it trivial to then add other kinds of validation
  that Schematron makes easy.  So attempting to do too much in XSD,
  rather than being conservative with XSD and conservative in Schematron.
  may actually reduce your choices for validation!
   5) Having decided to augment your grammar-based schema with Schematron
   and use XSD conservatively for the global schema, there may be less reason
   to actually use or mandate XSD: you might stick with DTDs, or if you need
   datatyping use RELAX NG. Or, allow locals to convert their global XSD
   schema into whatever they want. 

Another downside is that if you go outside XSD for basic structural constraints,
you lose the potential for some of the efficiency: however, of course, you
applications may not be those that could make use of that potential anyway. 
For example, there is no TAI (e.g. SPVI) DOM around, and XQuery is not
finished, and even when they are they may not be relevant to you.  But, of
course, they may be, too.

Rick Jelliffe


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