Re: XPath/XSLT 2.0 concerns
Hi Joerg, >> XSLT processors could do the kind of optimisation you're talking >> about *right now*, based on DTDs. Do they? If they don't, then why >> not? > > Apart from the problem that DTD related optimisations are hard to do > locally, I guess one reason is that the DTD analysis and the > appropriate optimisations have to be done a run time rather than at > compile time. 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. Though I would say that in XSLT, compile time and run time are usually the same. Of course there are environments where XSLT stylesheets get cached and reused, but in the majority of cases they're not. (This is a big contrast with the expected use of XQuery, I think -- one of the reasons why if optimisation is *ever* worthwhile, it's likely to be a lot more worthwhile in XQuery than it is in XSLT.) 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. Cheers, Jeni --- Jeni Tennison http://www.jenitennison.com/
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