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[xsl] XPath 2.0 expression that detects a cycle of references?


Subject: [xsl] XPath 2.0 expression that detects a cycle of references?
From: "Costello, Roger L. costello@xxxxxxxxx" <xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx>
Date: Fri, 25 Mar 2016 16:04:48 -0000

Hi Folks,

This XML document has id-idref references that create a circular dependency:

<document>
    <item id="HF">
        <title>Huckleberry Finn</title>
        <for-more-info idref="MT"/>
    </item>
    <item id="MT">
        <name>Mark Twain</name>
        <for-more-info idref="HF"/>
    </item>
</document>

I want an XPath expression which returns true if there is an <item> element
that contains a <for-more-info> element with an idref reference that
ultimately loops back around to the <item> element. For the above XML
document, the XPath expression should return true. Here's an XPath expression
that seems to work as desired:

for $i in /document/item return
      for $j in $i/for-more-info return
            for $k in /document/item[@id eq $j/@idref] return
                  if ($k/for-more-info/@idref eq $i/@id) then true() else ()

That XPath expression works fine when the cycle is between two <item> elements
but it doesn't work when the cycle is between three or more <item> elements.
Is there a way to write an XPath 2.0 expression to detect a cycle, regardless
of how big the cycle is?  /Roger

This XML has a cycle between three <item> elements:

<document>
    <item id="HF">
        <title>Huckleberry Finn</title>
        <for-more-info idref="MT"/>
    </item>
    <item id="MT">
        <name>Mark Twain</name>
        <for-more-info idref="SP"/>
    </item>
    <item id="SP">
        <publisher>Springer</publisher>
        <for-more-info idref="HF"/>
    </item>
</document>


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