The external file is accessed via the document('...') function.
My question number 1: Do XSLT processors cache external
referenced XML files?
Probably not, but obviously it depends on the processor. However, most
processors allow you to preload the document from the calling API. You may
find it better to supply the lookup document as the value of a stylesheet
parameter; if you do it using the document() function you can implement a
URIResolver or equivalent that maintains the cache.
Question number 2: Do you recommend any strategies to
optimise the query to the external XML file? I have
considered the following, but I am unsure as how each of them
can improve performance:
- Using the xsl:key + key function on the external
document('...') file.
- Implement the lookup table in a XSL file, specifying the
mappings outside the <xsl:templates> so that they are not
rendered.
Using keys will generally improve performance significantly, unless you are
using a processor like Saxon-SA that does the optimization automatically. I
can't see how your other idea would help.
Michael Kay
http://www.saxonica.com/
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