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Re: XPath/XSLT 2.0 concerns

Re:  XPath/XSLT 2.0 concerns
Hi Joerg,

>> Right, good point -- because the DTD information comes from the
>> source document. The stylesheet doesn't itself say "this is the DTD
>> that the source document uses". If it did, then it could make the
>> optimisations at compile time.
> Maybe add "possibility to declare a schema for source documents" to
> the XSLT2.0 requirements grab-bag? :-)

I think that it's there, or nearly there. See:



(and direct comments to public-qt-comments@w...).
>> Also, if you have compile-time optimisation of a 2.0 stylesheet or
>> query, effectively ignoring code that "couldn't possibly" be
>> relevant, you do have problems when you have a partially valid
>> document. If you want to be able to handle partial validity, you
>> can't really "optimise away" chunks of code because the basis of
>> your optimisation isn't necessarily true.
> I don't understand this. Currently, no XSLT processor I know of uses
> schema dependent optimisations, or even seriously thinks about this
> topic.

Sure, but there's a lot of stuff being put into XPath 2.0 precisely so
that XSLT processors *can* do this schema-dependent optimisation. I'm
trying to get at whether that stuff is worthwhile or not.

> And of course if someone did, it would only work on documents which
> are valid according to the schema. If a source XML document weren't
> valid, it would result in a fatal error even before the
> transformation starts.


So the picture that I have is that optimisation is probably only
useful if:

  - the schema of the source document is known at compile time
  - the stylesheet/query is compiled once, used many times
  - the source documents are completely valid

and even then, it's utility hasn't yet been proven empirically.



Jeni Tennison


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