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   Re: [xml-dev] UPA and schema handling

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Joe English wrote:
> But even SGML doesn't require conforming systems to report
> this condition; [4.267] says an ambiguous content model is not
> a "reportable markup error".
> (That's probably because nobody knew *how* to detect this condition
> until 1992 when Anne Bruegemann-Klein figured it out, but still...)

Lots of people knew how to detect it, but they all did it differently. 
Bruegemann-Klein's great contribution was to provide a rigorous 
definition for the condition. (She then went on to show that if a 
grammar was deterministic by her definition, a DFA could be built for it 
in linear time. That was pretty nice, too.)

> Anyway, AIUI the consensus in the SGML world was that
> the prohibition against ambiguous content models was
> overly restrictive and unnecessary.  That W3C XML Schema
> retained the restriction was a big mistake, IMO, one
> that could easily have been avoided by not conflating
> validation with annotation.

You are so right. Look where it got us. XML Schema. Strongly typed XQuery.

Bob Foster


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