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   RE: Again wit da AND and Repetitions

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  • From: Kay Michael <Michael.Kay@icl.com>
  • To: xml-dev@ic.ac.uk
  • Date: Fri, 14 May 1999 10:10:56 +0100

> XML requires deterministic content models. This allows 
> validators to do their job without having to look more than one element
> or do brute force tree searches.

It's not what XML requires that counts, it's what users require. What you're
saying is that if you have an integrity constraint that XML parsers are
congenitally incapable of enforcing, you had better implement it yourself,
the hard way, in the application.

I don't remember SQL ever adopting the view that the only integrity
constraints you were allowed to specify were those that could be evaluated
in linear time. In fact, the refusal to build implementation-based
limitations into the language was one of the major reasons for the success
of SQL.

(In implementing GedML I discovered that the integrity constraints that I
could specify in the DTD were such a pathetic subset of the total that I
might as well do all the validation in the application and ignore the DTD
capabilities entirely - especially as I had no way via the SAX API of
knowing whether the parser had done any validation or not).

Mike Kay

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