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: http://www.w3.org/TR/xslt20/#section-Stylesheets-and-Schemas and: http://www.w3.org/TR/xslt20/#import-schema (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. OK. 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. Cheers, Jeni --- Jeni Tennison http://www.jenitennison.com/
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