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Re: [xsl] Using 'collection'


Subject: Re: [xsl] Using 'collection'
From: "Mark Wilson pubs@xxxxxxxxxxxx" <xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx>
Date: Sat, 29 Aug 2015 16:38:32 -0000

Hi Michael,
I downloaded BaseX as suggested earlier, but can see that it and my XQuery learning curve are going to be steep. Since I will only be doing this process once (for the Royal Philatelic Society London, actually), I think I would rather try XSLT.
Thanks for the tip,
Mark


On 8/29/2015 8:59 AM, Michael Kay mike@xxxxxxxxxxxx wrote:
Its worth putting the data in an XML database such as BaseX if youre going to use it often enough to justify the cost of database loading. If you just want to use it once, e.g. to extract a subset of the data, then collection() should do the job - either in XQuery or XSLT.

To keep memory usage down, assuming youre implementing with Saxon, the simplest way is to ensure that each document is unloaded from memory as soon as it has been processed, which you can do with saxon:discard-document:

<xsl:for-each select=collection(docs?select=*.xml)>
   <xsl:apply-templates select=saxon:discard-document(.)>
</xsl:for-each>

discard-document() is a pseudo-function that returns a document unchanged, but with the side effect that it is marked as available for garbage collection.

Streamed processing is an alternative - but unfortunately in Saxon (until the next release) streaming cant be used together with collection().

Michael Kay
Saxonica


On 29 Aug 2015, at 15:25, Mark Wilson pubs@xxxxxxxxxxxx <xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx> wrote:

Hi Elliot,
I have never used XQuery or BaseX and will look into that, but what you have said about the XSLT looks good. I will try to sort this out and see where it goes. Thanks for taking the time.
Regards,
Mark

On 8/29/2015 7:13 AM, Eliot Kimber ekimber@xxxxxxxxxxxx wrote:
This sounds like a job better done using XQuery. A quick solution would be
to install BaseX and use its GUI to load your XML files and then apply the
query you need to the loaded docs. If you have to do complex
transformations on the things you find you can have the XQuery emit an XML
file that you can then apply an XSLT to, rather than trying to implement
the transform entirely in XQuery.

With XSLT and Saxon you could do something like:

<xsl:stylesheet ...>

<xsl:template name="run">
   <xsl:apply-templates select="collection('docs?select=*.xml')"/>
</xsl:template>

<xsl:template match="/">
   <!-- do stuff to find what you want in each doc -->
</xsl:template>
</xsl:stylesheet>

Then use the -i flag for Saxon to specify the initial template to run
("run").

The size of the documents shouldn't be a big issue, especially if you can
allocate sufficient memory to the processor. You could probably take
advantage of new streaming features in XSLT 3 and implemented in the
latest Saxon versions.

For something like this you might have to see how much virtual memory the
process requires by running it and if it fails with an out-of-memory
error, give it more until it either runs or you've run out of available
real memory.

Cheers,

Eliot

----
Eliot Kimber, Owner
Contrext, LLC
http://contrext.com




On 8/29/15, 8:36 AM, "Mark Wilson pubs@xxxxxxxxxxxx" <xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx> wrote:

I have been asked to isolate two elements each from a set of individual
xml files containing hundreds of elements. I thought collect() would
work, but each individual file is very large (36,000 + lines) and there
are 8000 of them. I have no idea as how to begin. I would include a
sample file, but as I said, they are very large. Where might I look to
get ideas?
Thanks,
Mark


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