Re: XSLT 2.0 Idea: third argument for key()

["G. Ken Holman" <gkholman@xxxxxxxxxxxxxxxxxxxx>]

At 00/09/04 19:56 +0100, Jeni Tennison wrote:
> In brief: I'd like to suggest having a third argument for key(), a node
> set, such that the key only retrieves nodes with the relevant key value
> that are within this node set.

When the node set is subset based entirely on hierarchy, I do this today 
using generate-id() based on the premise that generate-id() produces a name 
token (that never includes a space).

> Here's an example of the second area in which this would be useful,
> restricting nodes to a known node set: say I had a document with a massive
> dataset like:
>
> <athletes>
>   <country id="GRB">
>     <athlete event="100 metres">...</athlete>
>     <athlete event="200 metres">...</athlete>
>     <!-- another 400 athletes -->
>   </country>
>   <country id="ROI">
>     <athlete event="100 metres">...</athlete>
>     <athlete event="800 metres">...</athlete>
>     <!-- another 400 athletes -->
>   </country>
>   ...
> </athletes>
>
> I want to put the details of the athletes in a table, with columns being
> countries and rows being events, so I use a key to index on the event, and
> access the data for the table using:
>
>   key('athletes', @event)[generate-id(parent::country) =
>                           generate-id(current()/parent::country)]
>
> or something similar.  It would be a lot cleaner to do:
>
>   key('athletes', @event, parent::country/child::athlete)

What I would do in this case is:

...
<!ENTITY lookup-athletes
         "concat( generate-id(parent::country), ' ', @event )>
...
<xsl:key name="athletes" match="athlete"
         use="&lookup-athletes;"/>
...
  key('athletes', &lookup-athletes;)
...

> Any thoughts?  Objections?  Implementation issues?

Below are fragments from the solution to one of the exercises in my two-day 
hands-on course where students are required to group hockey team statistics 
based on the number of games played within either their division or their 
conference (two separate tables).

The Muenchian Method of grouping uses *all* members of the source node tree 
which isn't *directly* applicable since the grouping has to be subset by 
the hierarchy.  What I do is calculate the key table value to include the 
generated id of the ancestral point in the source node tree.  The space 
delimiter ensures no possible ambiguity in the concatenated value (provided 
all values are calculated the same way ... which I do using a general 
entity to ensure I don't screw up my typing).

...
<!DOCTYPE xsl:stylesheet [
                <!--use entities to keep typing down and promote 
consistency-->
<!ENTITY lookup-games-division
         "concat( generate-id(ancestor::division), ' ', g)">
<!ENTITY lookup-games-conference
         "concat( generate-id(ancestor::conference), ' ', g)">
]>
<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform";
                version="1.0">

<xsl:key name="games-division" match="team"
         use="&lookup-games-division;"/>    <!--games played within 
division-->
<xsl:key name="games-conference" match="team"
         use="&lookup-games-conference;"/><!--games played within 
conference-->

...
        <xsl:for-each select="division">
          <h3><xsl:value-of select="name"/> Division</h3>
          <xsl:for-each select=".//team
               [generate-id(.)=generate-id(key('games-division',
                                               &lookup-games-division;)[1])]">
...
                <xsl:for-each
                      select="key('games-division',&lookup-games-division;)">
...
        <h2><xsl:value-of select="name"/> Conference</h2>
        <xsl:for-each select=".//team
               [generate-id(.)=generate-id(key('games-conference',
                                              &lookup-games-conference;)[1] 
&lookup-games-conference;)[1])]">
...
                <xsl:for-each
                  select="key('games-conference',&lookup-games-conference;)">
...

The above works quite smoothly and is the basis of how I teach students to 
group subsets of the source node tree (after teaching the Muenchian Method 
of grouping all found members in the source node tree).

I hope this helps.

.................... Ken


--
G. Ken Holman                    mailto:gkholman@xxxxxxxxxxxxxxxxxxxx
Crane Softwrights Ltd.             http://www.CraneSoftwrights.com/s/
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