Re: [xsl] what to do if id() doesn't recognize xml:id

[Michael Kay <mike@xxxxxxxxxxxx>]

On 14/01/2011 09:55, TW wrote:
> I'm currently fathoming what's possible with keys as they are really
> quite handy.  I'm not sure yet whether I fully understand how they
> work.  In a short flash of excitement I thought I could do something
> like the following:  If I have data like this
>
> <?xml version="1.0"?>
> <?xml-stylesheet type='text/xsl' href='xsl/musx2svg.xsl'?>
> <children>
>    <mother xml:id="mother1" name="Laura">
>      <child father="father1" name="Kim"/>
>      <child father="father2" name="Peter" />
>    </mother>
>    <mother xml:id="mother2" name="Sarah">
>      <child name="Ron" father="father2" />
>    </mother>
>    <father xml:id="father1" name="Jim">
>      <child mother="mother1"/>
>    </father>
>    <father name="George"/>
> </children>
>
> where children can either be stored as child elements of their mothers
> or fathers, I could maybe directly select the mother of the current
> <child>  element like "key('mother',.)" regardless of how they are
> stored if I was using a key like
>
> <xsl:key name="mother" match="mother" use="child|//child[@mother =
> current()/@xml:id]"/>
Well, for starters, it's a pretty strange way of representing your data.

But I think you're making it too complicated. Define a simple key

<xsl:key name="id" match="*" use="xml:id"/>

and then a function

<xsl:function name="mother" as="element(mother)*">
<xsl:param name="child" as="element(child)"/>
<xsl:sequence select="$child/parent::mother | key('id', $child/@mother)"/>
</xsl:function>

Michael Kay
Saxonica

> But then I realized that not the nodes themselves from the node-set
> that's returned by "child|//child[@mother = current()/@xml:id]" would
> work as keys, but their string values would.  Unfortunately something
> like "generate-id(child|//child[@mother = current()/@xml:id])" would
> of course destroy the effect as only for for the first element of the
> node-set a key would be generated.
>
> So I figured I could add IDs to all<child>  elements in an additional
> processing step and use a key like
>
> <xsl:key name="mother" match="mother"
> use="child/@xml:id|//child[@mother = current()/@xml:id]/@xml:id"/>
>
> But there are potential problems if there
>
> (Of course in this made up example one could as well use
> "(parent::mother|key('id',@mother))".  However my intent is not to
> solve a special example case.  I'd like to get a clearer idea of where
> keys are applicable and where they aren't.)
>
> Thomas W.