View Source: MuenchianMethod - Waikato Linux Users Group

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The MuenchianMethod is a technique in [XSLT], which could probably also be applied to other data-centric Category:FunctionalProgrammingLanguages. It was developed/discovered by Steve Muench.

In [XSLT] a common problem is how to fire an action exactly once for each class of element seen. This is difficult in [XSLT] because it is a purely functional language and "remembering" that you've already seen an element of a class is impossible. There are certain highly recursive methods to solve the problem but these are incredibly inefficient, because (somewhat unusually for a functional language) [XSLT] is optimised not for recursion but for application of [Template]s to nodes in the [XML] tree.

The MuenchianMethod avoids this problem using a key defined to classify elements into a class. Keys in [XSLT] are like indexes in SQL -- they are efficient. A good introduction to the MuenchianMethod can be [found on the web | http://www.jenitennison.com/xslt/grouping/index.xml].

As an example, the following code creates a key called kName based on the name of each node. The template then matches only those nodes which are the first node in the key with that name.

  ...
  <xsl:key name="kName" match="*" use="name()"/>
  ...
  <xsl:template match="*[generate-id()
                        = generate-id(key('kName',
                                          name()
                                          )[[1]
                                      )
                        ]">
    Element name: <xsl:value-of select="name()"/>
    <xsl:apply-templates/>
  </xsl:template>
  ...

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XSLT

Last edited on Thursday, November 6, 2003 9:19:57 am by MuenchianMethod

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