Subject: RE: efficiency with id()
From: "Michael Kay" <mhk@xxxxxxxxx>
Date: Thu, 3 Jul 2003 12:13:05 +0100
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The answer to performance questions is always to measure it and see. You
won't necessarily get the same results from two different processors.
I would expect id() and key() to give similar performance, but if the
attribute is an ID then there's no point also defining it as a key, that
would just give you two indexes; a processor won't normally build an
index for a key unless you actually use it, but this may or may not be
true for IDs.
If your task is to load the document from disk and extract a single
element, then an index isn't going to help you much because the cost of
building it outweighs the benefit it gives you. You might as well use a
straight predicate, such as //p[@id='xyz'].
Michael Kay
> -----Original Message-----
> From: owner-xsl-list@xxxxxxxxxxxxxxxxxxxxxx
> [mailto:owner-xsl-list@xxxxxxxxxxxxxxxxxxxxxx] On Behalf Of
> James Cummings
> Sent: 03 July 2003 10:41
> To: xsl-list@xxxxxxxxxxxxxxxxxxxxxx
> Subject: efficiency with id()
>
>
> Ok, let's say you have a file of:
> -----
> <?xml version="1.0"?>
> <foo>
> <bar>
> <blort>
> <p id="c1001"><body wit="A B C">This is a
> <app><rdg wit="A B">test</rdg><rdg
> wit="C">really big test</rdg></app>
> but only a test!</body></p>
> <p id="c1002"><body wit="A B C">This is a
> <app><rdg wit="A B">test</rdg><rdg
> wit="C">really big test</rdg></app>
> but only a test!</body></p>
> <p id="c1003"><body wit="A B C">This is a
> <app><rdg wit="A B">test</rdg><rdg
> wit="C">really big <add> place="supra">test</add></rdg></app>
> but only a test!</body></p>
> ...
> <p id="c9205"><body wit="A B C">This is a
> <app><rdg wit="A B">test</rdg><rdg
> wit="C">really <gap/>test</rdg></app>
> but only a test!</body></p>
> </blort>
> </bar>
> </foo>
> -----
>
> What is the most efficient/quickest way of grabing a copy-of
> a particular <p> (and
> children) by its @id?
>
>
> Is it best to do something like:
> -----
> <xsl:template match="/">
> <xsl:copy-of select="id($id)"/>
> </xsl:template
>
> <!-- and another empty template matching anything you don't
> want to display -->
> -----
>
> or is there a quicker way? Is key() quicker? The @id is in
> reality declared as type ID, so seems reasonable to use that.
> (This is for a quite large (well 2.5meg), file, which
> admittedly would probably be better just burst out into
> seperate files for each <p> element in this example.) Any
> suggestions appreciated.
>
> -James
>
> ---
> Dr James Cummings, James.Cummings@xxxxxxxxx,
> http://www.uea.ac.uk/~q503 Cursus Project, > School of Music,
> University of East Anglia, Norwich, Norfolk, NR4 7TJ, UK
> Tel:(01603)593-595
>
>
>
> XSL-List info and archive: http://www.mulberrytech.com/xsl/xsl-list
>
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