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   Re: [xml-dev] XPath/XSLT 2.0 concerns

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Hi Mike,

> Well, the more I think about it, the more I think that people are
> actually using match patterns as a sort of "structural type
> detection" mechanism. People write template rules that say "when I
> get one of these, do this", and they are defining "one of these" by
> means of a pattern that is in effect a type. Now very often there's
> a one-to-one mapping between these types and element names, so the
> patterns are very simple. But I think that once people are dealing
> with really large vocabularies, constructing the patterns in terms
> of element names gets more and more difficult, and being able to
> match against types at different levels of a type hierarchy gets
> more and more valuable.

I agree with this, very much. Actually I think we can break this
pattern down into two classes:

  1. grouping elements based on their *content* -- in other words, the
     *type* hierarchy

  2. grouping elements based on their *context* -- in other words, the
     *substitution group* hierarchy

An example of 1 is dealing with all addresses in the same way, whether
the element that holds the address is a <buyerAddr> or <supplierAddr>

An example of 2 is dealing with all block-level elements in the same
way, whether they're paragraphs, tables or lists (all of which have
very different content).

There might be different proportions of 1 and 2 in different kinds of
structures -- more of 1 in data-oriented structures, more of 2 in
document-oriented structures; I'm not sure. Certainly, looking at the
stylesheets I've written recently, I see use cases for both kinds. The
current focus in XPath/XQuery is very much on 1 rather than 2.



Jeni Tennison


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