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RE: variables vs. modes

2004-11-25 16:47:10
I tend to use this approach quite heavily, of structuring the processing as
a sequence of variables, each one of which is derived from the one before.
It's like a miniature pipeline. Some people use the same technique but using
local variables within a containing template, rather than using global
variables.

However, as soon as you have more than one step in your pipeline that can
benefit from the flexibility of apply-templates, you need to think in terms
either of multiple modes within a single stylesheet, or multiple stylesheets
connected in a pipeline.

Incidentally I've had some brief exposure recently to Orbeon as a pipeline
processor for stringing together transformations, and it's well worth a
look.

Michael Kay
http://www.saxonica.com/

-----Original Message-----
From: Bruce D'Arcus [mailto:bdarcus(_at_)myrealbox(_dot_)com] 
Sent: 25 November 2004 22:03
To: xsl-list(_at_)lists(_dot_)mulberrytech(_dot_)com
Subject: [xsl] variables vs. modes

I'm considering reworking my (2.0) stylesheets towards 
greater reliance 
on global variables.

In my current approach, I use multiple passes, with multiple modes.  
However, I feel that it may make more sense (be more flexible, easier 
to integrate with other stylesheets and to maintain, etc.) to use 
variables instead.  Below is a simple example of what I mean.

Are there any counter-arguments I may be missing before I actually do 
this?

Bruce

<?xml version="1.0" encoding="utf-8"?>
<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform"; 
version="2.0"
    xmlns:mods="http://www.loc.gov/mods/v3";
    xmlns:db="http://docbook.org/docbook-ng";
    xmlns:exist="http://exist.sourceforge.net/NS/exist";
    exclude-result-prefixes="db mods exist">

    <xsl:output method="xml" encoding="utf-8" indent="yes"/>

<!-- grab all the citation pointers -->
    <xsl:variable name="citerefs" select="//db:biblioref/@linkend"/>

<!-- construct a list of unique references to pass to a query -->
    <xsl:variable name="citekeys">
      <xsl:text>(</xsl:text>
        <xsl:for-each-group select="$citerefs" group-by=".">
          <xsl:if test="position() &gt; 1">,%20</xsl:if>
          <xsl:text>'</xsl:text>
          <xsl:value-of select="."/>
          <xsl:text>'</xsl:text>
        </xsl:for-each-group>
      <xsl:text>)</xsl:text>
    </xsl:variable>

<!--
take list of references, and grab them from a database over http; in 
this case it's an XQuery to eXist,
but it should be parameterized for flexibility
-->
    <xsl:variable name="bibrecord"
      
select='doc(concat("http://localhost:8080/exist/servlet/db/biblio?";,
              
"_query=declare%20namespace%20mods=%22http://www.loc.gov/mods/v3%22;";,
              "%20for%20$citekey%20in%20",
                      $citekeys,
              
"%20return%20/mods:modsCollection/mods:mods[(_at_)ID=$citekey]"))' />
<!--
create raw bib collection; in a real implementation, this 
might be where
enhancement (grouping, sorting, adding content for processing, etc.) 
would take place
-->
    <xsl:variable name="raw-biblist">
      <mods:modsCollection>
        <xsl:copy-of select="$bibrecord/exist:result/mods:mods" />
      </mods:modsCollection>
    </xsl:variable>

<!-- take raw biblist and format it -->
    <xsl:variable name="formatted-biblist">
      <xsl:for-each 
select="$raw-biblist/mods:modsCollection/mods:mods">
        <p id="{(_at_)ID}">
          <xsl:apply-templates select="mods:titleInfo"/>
        </p>
      </xsl:for-each>
    </xsl:variable>

    <xsl:template match="/">
      <div id="bibliography">
        <xsl:copy-of select="$formatted-biblist"/>
     </div>
    </xsl:template>

    <xsl:template match="mods:titleInfo">
      <span class="title">
        <xsl:apply-templates select="mods:title"/>
        <xsl:apply-templates select="mods:subTitle"/>
      </span>
    </xsl:template>

    <xsl:template match="mods:title">
      <xsl:value-of select="."/>
    </xsl:template>

    <xsl:template match="mods:subTitle">
      <xsl:text>: </xsl:text>
      <xsl:value-of select="."/>
    </xsl:template>

</xsl:stylesheet>


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