Multiple level filtering with XSLT

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Hello,

I am developing a generic filtering stylesheet that needs to apply any number
of filters to an XML data source. The filters can be applied at any level of
the hierarchy.

On to the example... Say I have an XML file (see below) that I need to filter.
I want to filter out 'c' elements where '@x=1' and I also want to filter out
'd' elements where '@x>=7'. Problem is that when the 'd' elements are filtered
out, I am left with a 'c' element that contains no 'd' elements, this is not
allowed according to the XSD (must have at least 1 'c' in each 'd').

Please note:
* I have no access to modify the XSDs
* Filtering at any other step in the process (DB/xml source generation) is not
an option I have available.

To illustrate my example:
Start with the following XML file
<a x="1">
 <b x="1">
  <c x="1">
   <d x="1"/>
   <d x="2"/>
  </c>
  <c x="2">
   <d x="3"/>
   <d x="4"/>
   <d x="5"/>
  </c>
  <c x="3">
   <d x="6"/>
   <d x="7"/>
  </c>
  <c x="4">
   <d x="8"/>
   <d x="9"/>
  </c>
 </b>
</a>

After applying my XSL I end up with the following. Note the empty 'c' element.
I somehow need to exclude the 'c' elements that have had all their 'd'
elements filtered out.
<a x="1">
 <b x="1">
  <c x="2">
   <d x="3"/>
   <d x="4"/>
   <d x="5"/>
  </c>
  <c x="3">
   <d x="6"/>
  </c>
  <c x="4" />
 </b>
</a>

The XSL that I have currently (below) will work well if filtering occurs at
the same level, but will not work reliably when filtering occurs at multiple
levels.
<?xml version="1.0" encoding="UTF-8" ?>
<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
version="1.0">
    <xsl:template match="*">
        <xsl:choose>
		<!-- first filter -->
            <xsl:when test="local-name()='c'">
                <xsl:if test="not(@x=1)">
                    <xsl:copy>
                        <xsl:copy-of select="@*"/>
                        <xsl:apply-templates/>
                    </xsl:copy>
                </xsl:if>
            </xsl:when>
		<!-- second filter -->
            <xsl:when test="local-name()='d'">
                <xsl:if test="not(@x&gt;=7)">
                    <xsl:copy>
                        <xsl:copy-of select="@*"/>
                        <xsl:apply-templates/>
                    </xsl:copy>
                </xsl:if>
            </xsl:when>
            <xsl:otherwise>
                <xsl:copy>
                    <xsl:copy-of select="@*"/>
                    <xsl:apply-templates/>
                </xsl:copy>
            </xsl:otherwise>
        </xsl:choose>
    </xsl:template>
</xsl:stylesheet>


Any help or guidance would be greatly appreciated!

Thanks,
Jeff.


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