Subject: Re: [xsl] Cost of complex match patterns From: "Andrew Welch" <andrew.j.welch@xxxxxxxxx> Date: Tue, 12 Aug 2008 11:20:03 +0100 |
>> match="foo[//bar]" > >> match="foo" > >> Should the former be avoided, or because it's within a match >> pattern it's converted to a simple lookup so it's fine? > > I don't know the details of your processor on that point, but out of > interest, if you only match on the main input tree, you can replace the > former by: > > <xsl:variable name="has-bar" as="xs:boolean" select=" > exists(//bar)"/> > > <xsl:template match="foo[$has-bar]"> Indeed (apart from 1.0 where you can't use variables in match patterns)... the question I'm asking though is whether you need to workaround potentially expensive match patterns (as they will be evaluated per element), or whether through the inbuilt pattern matching process it's actually a good idea to move work into the match pattern. For example, match="foo[ancestor::bar/@type = 'A']" and match="foo[ancestor::bar/@type = 'B']" (or "bar[@type = 'A']//foo" but I prefer the above) Is it better to pass down the type through parameters to avoid the predicate, or is there no need to worry about it because it becomes a simple lookup? I'm pretty sure it's the latter.... -- Andrew Welch http://andrewjwelch.com Kernow: http://kernowforsaxon.sf.net/
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