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Re: [xsl] Nested filters, or filter too complicated.
2018-01-17 11:08:10
The "ambiguous rule match" doesn't mean there's anything wrong with this
pattern, it means there is more than one pattern that matches the same nodes,
and you haven't labelled them with a priority value to indicate which one wins.
Michael Kay
Saxonica
On 17 Jan 2018, at 16:53, Kerry, Richard
richard(_dot_)kerry(_at_)atos(_dot_)net
<mailto:richard(_dot_)kerry(_at_)atos(_dot_)net>
<xsl-list-service(_at_)lists(_dot_)mulberrytech(_dot_)com
<mailto:xsl-list-service(_at_)lists(_dot_)mulberrytech(_dot_)com>> wrote:
Michael, Martin,
Thank you both for your replies.
I knew the text() entries were not necessary but I'd left them in for clarity
(*). I had missed (ie not realized) the issue about string-values, comments,
etc.
Martin, both of your versions gave "Ambiguous rule match".
Michael, having fixed one minor error, a spurious extra ')' immediately
before the final ']', I found that your version also gave "Ambiguous rule
match".
On giving a priority of 1 to the simpler filter and 2 to all your various
suggestions I am now finding it is working and giving the result I want (ie
all three options work).
Was the ambiguous rule match because both are just classed as having a
filter, and the rule selection doesn't care that one has a more complex
filter than the other?
I had sort of realized that I was doing a join, though as I have very little
experience of database work I hadn't thought to use the term.
I am using Saxon 9.8.0.3 so XSL 2 is fine. I think 3 would be too but I only
have experience as far as 2.
So thank you both, I am now able to get the results that I need.
Regards,
Richard.
(*) clarity in the sense that although it was more verbose I thought it made
my intent clearer.
Richard Kerry
BNCS Engineer, SI SOL Telco & Media Vertical Practice
T: +44 (0)20 3618 2669
M: +44 (0)7812 325518
4 Triton Square, Regent’s Place, London NW1 3HG
richard(_dot_)kerry(_at_)atos(_dot_)net
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From: Michael Kay mike(_at_)saxonica(_dot_)com
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Sent: 17 January 2018 16:29
To: xsl-list(_at_)lists(_dot_)mulberrytech(_dot_)com
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Subject: Re: [xsl] Nested filters, or filter too complicated.
You're trying to do a join. That involves comparing items from two different
sets.
In SQL (and in mathematical predicate logic) you do this by binding "range
variables" to the items in each set, and then using predicates such as
where X.ref = Y.id
You can use the same approach in XSLT, but with caveats. Only with XSLT 3.0
are you allowed to bind variables within an XPath expression. But that's
where "." and "current() come in. Within a predicate, "." is used as an
implicit range variable for the set you are filtering. You can also sometimes
use "current()" as your second range variable. Or you can bind variables
explicitly using xsl:variable. The problem about using ".", however, is that
it changes its meaning in a nested predicate.
In this case in XSLT 2.0 upwards, current() rescues you:
match="type[.='Action'][$data/device-description/param[@name=current()/../base-name]/@standard='no')]
"
(Note I've avoided the use of text() here. It's much better to compare with
the string-value of the element, rather than with its text nodes - it will
continue to work, for example, if the text is split up by comments).
XSLT 2.0 defines that current() within a pattern refers to the node being
tested against the pattern. Unfortunately though (IIRC), XSLT 1.0 didn't
allow use of current() in patterns. But no-one is still using XSLT 1.0, are
they???
Michael Kay
Saxonica
On 17 Jan 2018, at 15:19, Kerry, Richard
richard(_dot_)kerry(_at_)atos(_dot_)net
<mailto:richard(_dot_)kerry(_at_)atos(_dot_)net>
<xsl-list-service(_at_)lists(_dot_)mulberrytech(_dot_)com
<mailto:xsl-list-service(_at_)lists(_dot_)mulberrytech(_dot_)com>> wrote:
I am trying to use XSLT to process one XML file, which refers to data in
another, and I am having trouble with getting a filter to work.
The first source file (device.xml) - the one that is actually processed by
the XSL - has entries like this:
<device-description>
<device-value>
<base-name>PollNow</base-name>
<name>Poll Now</name>
<type>Action</type>
</device-value>
<device-value>
<base-name>StartupPollNow</base-name>
<name>Startup Poll Now</name>
<type>Action</type>
</device-value>
<device-value>
<base-name>Ping</base-name>
<name>Ping</name>
<type minimum-length="0" maximum-length="256" >String</type>
</device-value>
</device-description>
One of the templates is approximately as follows:
<x:template match="type[text()='Action']" >
<!-- do basic action. -->
</x:template>
This quite happily matches all the <device_name> elements where the <type>
has a text value pf "Action".
However, I have a second XML file (device-3.xml) which contains some data
that I wish to use to modify the behaviour of the transform. It has entries
like this:
<device-description>
<param name="PollNow" standard="no" >
<name>Poll Now</name>
<description>normal poll</description>
</param>
<param name="StartupPollNow" standard="no" >
<name>Startup Poll Now</name>
<description>startup poll</description>
</param>
<param name="Ping">
<name>Ping</name>
<description>Ping-Pong</description>
</param>
</device-description>
The second file is accessed via a variable, as follows:
<x:variable name="data" select="document($in-file-3)"/>
What I want to achieve is that for all <type> elements where there is a
corresponding <param> where base-name is the same as param/@name, I want a
different action.
The additional template I have for this is currently as follows
<x:template
match="type[text()='Action'][$data/device-description/param[@name=../base-name/text()]/@standard='no')]
" >
<!-- do different action. -->
</x:template>
My thinking is that the first filter is as with the first template I listed,
matching all <type> elements whose text is "Action".
The second filter should then enable me to pick the right param from the
second file, and do something based on the value of its @standard.
Maybe once I'm in the second filter I am causing confusion as to which
element the @name refers to (which should be the param) and which the
../base-name is relative to (the device-value/type)?
Can I do all this within a single template's @match ? Or am I making it too
complicated. In which case how might I get the result I'm looking for?
Appreciatively,
Richard.
The examples are all slightly simplified from the real data, which has more
elements, and the transforms are in a mode.
Richard Kerry
BNCS Engineer, SI SOL Telco & Media Vertical Practice
T: +44 (0)20 3618 2669
M: +44 (0)7812 325518
4 Triton Square, Regent’s Place, London NW1 3HG
richard(_dot_)kerry(_at_)atos(_dot_)net
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