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Re: [xsl] Question on duplicate node elimination

2010-08-22 17:12:58
I'm not sure what you find surprising about the results you are seeing.
What results would you expect?
Not surprising.

But how could the algorithm step of "duplicate elimination" be done?
How can the duplicates be determined and removed, correctly?

Perhaps I was not clear enough with my question.
How can this step (p. 40 from [1]) be implemented in XPath 1.0 plus
eslt:node-set():
A location step identifies a new mode-set relative to the context node-set.
The location step is evaluated against each node in the context node-set,
and the union of the resulting node-sets becomes the context node-set for
the next step. Location steps consist of an axis identifier, a node test
and zero or more predicates (see Figure 3-4). ...


[1]
http://www.theserverside.net/tt/books/addisonwesley/EssentialXML/index.tss

Mit besten Gruessen / Best wishes,

Hermann Stamm-Wilbrandt
Developer, XML Compiler, L3
WebSphere DataPower SOA Appliances
----------------------------------------------------------------------
IBM Deutschland Research & Development GmbH
Vorsitzender des Aufsichtsrats: Martin Jetter
Geschaeftsfuehrung: Dirk Wittkopp
Sitz der Gesellschaft: Boeblingen
Registergericht: Amtsgericht Stuttgart, HRB 243294



From:       Michael Kay <mike(_at_)saxonica(_dot_)com>
To:         xsl-list(_at_)lists(_dot_)mulberrytech(_dot_)com
Date:       08/22/2010 11:53 PM
Subject:    Re: [xsl] Question on duplicate node elimination



I'm not sure what you find surprising about the results you are seeing.
What results would you expect?

xsl:copy-of creates a new node. Copying the same node twice creates two
copies with distinct identity. Is that the issue?

Michael Kay
Saxonica

On 22/08/2010 22:25, Hermann Stamm-Wilbrandt wrote:
Hello,

I have a question on duplicate node elimination.

From the XPATH 1.0 specification:
...
* node-set (an unordered collection of nodes without duplicates)
...
An initial sequence of steps is composed together with a following step
as
follows. The initial sequence of steps selects a set of nodes relative to
a
context node. Each node in that set is used as a context node for the
following step. The sets of nodes identified by that step are unioned
together. The set of nodes identified by the composition of the steps is
this union.
...

So "are unioned together" results in a node-set and that does not contain
duplicates.

Now how can this algorithm step be realized in XPATH 1.0 plus
exslt:node-set
funtion?
(this would work in browsers with the technique from David Carlisle [1])


This is the output for below stylesheet simple.xsl on file simple.xml.
For the nodes four node /a/b/c their parents are copied into an
intermediate
result. But xsltproc and xalan show that the four nodes are different by
the
their generate-id() values, whereas the first pair and last pair are
representations of the same node.

xsltproc        xalan
1: id2659470    1: AbT0
2: id2659470    2: AbT0
3: id2659354    3: AbT1
4: id2659354    4: AbT1

1: id2659234    1: AbT2
2: id2659244    2: AbT3
3: id2659254    3: AbT4
4: id2659264    4: AbT5

1:<b>           1:<b>
     <c>1</c>         <c>1</c>
     <c>2</c>         <c>2</c>
   </b>             </b>
2:<b>           2:<b>
     <c>1</c>         <c>1</c>
     <c>2</c>         <c>2</c>
   </b>             </b>
3:<b>           3:<b>
     <c>1</c>         <c>1</c>
     <c>2</c>         <c>2</c>
   </b>             </b>
4:<b>           4:<b>
     <c>1</c>         <c>1</c>
     <c>2</c>         <c>2</c>
   </b>             </b>



$ cat simple.xml
<a>
   <b>
     <c>1</c>
     <c>2</c>
   </b>
   <b>
     <c>1</c>
     <c>2</c>
   </b>
</a>
$ cat simple.xsl
<xsl:stylesheet version="1.0"
   xmlns:xsl="http://www.w3.org/1999/XSL/Transform";
   xmlns:exsl="http://exslt.org/common";


   <xsl:output omit-xml-declaration="yes"/>

   <xsl:template match="/">
     <xsl:variable name="rtf">
       <xsl:for-each select="/a/b/c">
         <xsl:copy-of select=".."/>
       </xsl:for-each>
     </xsl:variable>

     <xsl:for-each select="/a/b/c">
       <xsl:value-of select="position()"/><xsl:text>:</xsl:text>
       <xsl:value-of select="generate-id(..)"/><xsl:text>&#10;</xsl:text>
     </xsl:for-each>

     <xsl:text>&#10;</xsl:text>

     <xsl:for-each select="exsl:node-set($rtf)/*">
       <xsl:value-of select="position()"/><xsl:text>:</xsl:text>
       <xsl:value-of select="generate-id(.)"/><xsl:text>&#10;</xsl:text>
     </xsl:for-each>

     <xsl:text>&#10;</xsl:text>

     <xsl:for-each select="exsl:node-set($rtf)/*">
       <xsl:value-of select="position()"/><xsl:text>:</xsl:text>
       <xsl:copy-of select="."/><xsl:text>&#10;</xsl:text>
     </xsl:for-each>
   </xsl:template>

</xsl:stylesheet>
$


[1] http://dpcarlisle.blogspot.com/2007/05/exslt-node-set-function.html


Mit besten Gruessen / Best wishes,

Hermann Stamm-Wilbrandt
Developer, XML Compiler, L3
WebSphere DataPower SOA Appliances
----------------------------------------------------------------------
IBM Deutschland Research&  Development GmbH
Vorsitzender des Aufsichtsrats: Martin Jetter
Geschaeftsfuehrung: Dirk Wittkopp
Sitz der Gesellschaft: Boeblingen
Registergericht: Amtsgericht Stuttgart, HRB 243294


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