XSLT evaluate XPath from a string

Mycroft

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Aug 19, 2008, 4:19:01 PM8/19/08

to

I need to pull XPath from strings obtained from the XML data source. A
typical query might look like:

XML:
<library>
<books>
<book title="A" type="science fiction"/>
<book title="B" type="fantasy"/>
<book title="C" type="romance"/>
<book title="D" type="science fiction"/>
<book title="E" type="Christianity"/>
</books>
<librarian>
<defaultXPath>//book[type="Christianity"]</defaultXPath>
</librarian>
</library>

XSLT (works):
<xsl:variable name="Books">
<xsl:apply-templates select="//book[type="Christianity"]"/>
</xsl:variable>

XSLT (fails):
<xsl:apply-templates select="//librarian/defaultXPath"/>
<xsl:apply-templates select="{//librarian/defaultXPath}"/>

The problem is that the apply-templates command process the string as a data
island rather than interpreting the string as an XPath query.

I have tried using code from EXSLT but that has not worked and everything I
read suggests that XSLT 2.0 might have a method to perform this operation,
but I find no examples.

Any suggestions?

Joe Fawcett

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Aug 20, 2008, 3:16:43 AM8/20/08

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XSLT 2.0 has no facility to do this either. Some processors have extension
functions built in that do this, Saxon for instance has saxon:evaluate(). If
you are using MSXML you can write an extension function in script, if using
XML.NET then you can use a .NET language.
It also might be useful to see what you tried in EXSLT that failed.

--

Joe Fawcett (MVP - XML)

http://joe.fawcett.name

"Mycroft" <Myc...@discussions.microsoft.com> wrote in message
news:C00EE749-5633-46D5...@microsoft.com...

Martin Honnen

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Aug 20, 2008, 7:04:35 AM8/20/08

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Mycroft wrote:

> I have tried using code from EXSLT but that has not worked and everything I
> read suggests that XSLT 2.0 might have a method to perform this operation,
> but I find no examples.

Saxon 9 is the current Saxon version that implements XSLT and XPath 2.0.
It has
http://www.saxonica.com/documentation/extensions/functions/evaluate.html
and
http://www.saxonica.com/documentation/extensions/functions/evaluate-node.html
so with your sample XML corrected to (you had 'type' instead of '@type'
which does not find anything)

<defaultXPath>//book[@type="Christianity"]</defaultXPath>
</librarian>
</library>

and a stylesheet with

<xsl:stylesheet
xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
xmlns:saxon="http://saxon.sf.net/"
exclude-result-prefixes="saxon"
version="2.0">

<xsl:template match="/">
<xsl:apply-templates
select="saxon:evaluate-node(library/librarian/defaultXPath)"/>
</xsl:template>

<xsl:template match="book">
<xsl:copy-of select="."/>
</xsl:template>

</xsl:stylesheet>

the output is

<?xml version="1.0" encoding="UTF-8"?><book title="E" type="Christianity"/>

--

Martin Honnen --- MVP XML
http://JavaScript.FAQTs.com/

Mycroft

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Aug 21, 2008, 2:56:10 PM8/21/08

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Joe,

You asked me why EXSLT failed to work…

I initially tried to use EXSLT which failed only because I stopped trying.
The software I found for it was from 2001 and required a 30-day trial license
key, which I did not have. So, while looking for other options I learned XSLT
2.0 was out and began researching it. I found comments about it that appeared
to address this exact “XPath from a string” issue so I posted the question on
this discussion board. I had been staying away from Saxon and EXSLT since
they incur additional software license fees and issues I did not want to deal
with (problems concerning software written for government use). Despite this,
it looks as though I will have to use Saxon or EXSLT until I find a .NET
alternative or can figure out how to code a custom solution.

I am uncertain whether I am using XML.NET or MSXML. I am writing the XML and
XSLT using VS 2005 and rendering it through IE7. So, I do not know which XML
engine it is using.

Sincerest thanks for your assistance.

Mycroft

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Aug 21, 2008, 3:00:03 PM8/21/08

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Martin,

Thank you for the code corrections! I wrote the example quickly without
testing it, to provide an example of what I was trying to do. I now have a
successful implementation using Saxon but using that incurs additional
licenses and security/legal issues.

Anyway, my code is working successfully using Saxon. It requires a different
approach but it is functional.

Do you know where I might find examples of linking the .NET XSLT engine to a
custom function library? Perhaps I can code a small DLL to evaluate the
variable just as Saxon does.

Many thanks for your most timely assistance.

Mycroft

Martin Honnen

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Aug 22, 2008, 7:24:51 AM8/22/08

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Mycroft wrote:

> Do you know where I might find examples of linking the .NET XSLT engine to a
> custom function library? Perhaps I can code a small DLL to evaluate the
> variable just as Saxon does.

If you are talking about System.Xml.Xsl.XslCompiledTransform then you
have two options, msxsl:script to write extension functions with C# or
VB.NET or JScript.NET:
http://msdn.microsoft.com/en-us/library/wxaw5z5e(VS.80).aspx
or extension objects passed in with an XsltArgumentList:
http://msdn.microsoft.com/en-us/library/tf741884(VS.80).aspx
For an example see the post by Anton Lapounov in
http://forums.microsoft.com/MSDN/ShowPost.aspx?PostID=1809134&SiteID=1

Note however that your other post talks about running the transformation
inside of IE 7, in that case the XSLT processor used is MSXML 3 and not
the .NET processor XslCompiledTransform.

Mycroft

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Aug 22, 2008, 10:01:00 AM8/22/08

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Fantastic link references. Many thanks for your assistance!