XSLT deepening content structure - xslt

Question

given the following structure:
<TITEL1>...</TITEL1>
<p>..</p>
<TITEL2>...</TITEL2>
<TITEL3>...</TITEL3>
<TITEL3>...</TITEL3>
<P>...<P>
is there a way to get to this:
<TITEL1>
<TITEL>...</TITEL>
<p>...</p>
<TITEL2>
<TITEL>...</TITEL>
<TITEL3>
<TITEL>...</TITEL>
<P>...</P>
</TITEL3>
<TITEL3>
<TITEL>...</TITEL>
<P>...</P>
</TITEL3>
</TITEL2>
</TITEL1>
or in other words,is there a way to have higher level titels inclose lower level titels and all content that follows them, thus creating a nested structure. The content of each TITEL1,2 and 3 tag should go into a new <TITEL>-element

Answer 1

With XSLT 2.0 (as implemented by Saxon 9 or AltovaXML tools) you can use xsl:for-each-group group-starting-with and a recursive function:
<xsl:stylesheet
xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
version="2.0"
xmlns:xsd="http://www.w3.org/2001/XMLSchema"
xmlns:mf="http://example.com/2010/mf"
exclude-result-prefixes="xsd mf">
<xsl:output indent="yes"/>
<xsl:function name="mf:nest" as="element()*">
<xsl:param name="elements" as="element()*"/>
<xsl:param name="level" as="xsd:integer"/>
<xsl:for-each-group select="$elements" group-starting-with="*[starts-with(local-name(), concat('TITEL', $level))]">
<xsl:choose>
<xsl:when test="self::*[starts-with(local-name(), concat('TITEL', $level))]">
<xsl:element name="TITEL{$level}">
<xsl:apply-templates select="."/>
<xsl:sequence select="mf:nest(current-group() except ., $level + 1)"/>
</xsl:element>
</xsl:when>
<xsl:otherwise>
<xsl:apply-templates select="current-group()"/>
</xsl:otherwise>
</xsl:choose>
</xsl:for-each-group>
</xsl:function>
<xsl:template match="ROOT">
<xsl:sequence select="mf:nest(*, 1)"/>
</xsl:template>
<xsl:template match="#* | node()">
<xsl:copy>
<xsl:apply-templates select="#* | node()"/>
</xsl:copy>
</xsl:template>
<xsl:template match="*[starts-with(local-name(), 'TITEL')]">
<TITEL>
<xsl:apply-templates select="#* | node()"/>
</TITEL>
</xsl:template>
</xsl:stylesheet>
With that stylesheet the input
<ROOT>
<TITEL1>Titel 1, 1</TITEL1>
<p>..</p>
<TITEL2>Titel 2, 1</TITEL2>
<TITEL3>Titel 3, 1</TITEL3>
<TITEL3>Titel 3, 2</TITEL3>
<P>...</P>
</ROOT>
is transformed to the output
<TITEL1>
<TITEL>Titel 1, 1</TITEL>
<p>..</p>
<TITEL2>
<TITEL>Titel 2, 1</TITEL>
<TITEL3>
<TITEL>Titel 3, 1</TITEL>
</TITEL3>
<TITEL3>
<TITEL>Titel 3, 2</TITEL>
<P>...</P>
</TITEL3>
</TITEL2>
</TITEL1>

Answer 2

There isn't a particularly eligant way of doing what you want. It's (probably) possible, but it would involve some pretty ugly (and slow) XPath queries using the following-sibling axis with filters on the preceding-sibling axis matching back to the current node.
If it's at all a possibility, I would recommend creating the hierarchy outside of XSLT (in C#, Java, etc)
If you choose to go down the scary path, you would be looking to do something like this (untested):
<xsl:template match="TITEL1">
<TITEL1>
<xsl:apply-templates
select="following-sibling::(p|TITEL2)[(preceding-sibling::TITEL1)[1]=.]" />
</TITEL1>
</xsl:template>
<xsl:template match="TITEL2">
<TITEL1>
<xsl:apply-templates
select="following-sibling::(p|TITEL3)[(preceding-sibling::TITEL2)[1]=.]" />
</TITEL1>
</xsl:template>
...
This is only an example, and I can already see problems with the match. Coming up with the final XPath query would be quite involved, if it's actually possible at all.

Answer 3

If you can't use XSLT 2.0, here is an XSLT 1.0 stylesheet that should produce the same result as the XSLT 2.0 stylesheet I posted earlier:
<xsl:stylesheet
xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
version="1.0">
<xsl:output indent="yes"/>
<xsl:template match="ROOT">
<xsl:apply-templates select="*[1]" mode="nest">
<xsl:with-param name="level" select="1"/>
</xsl:apply-templates>
</xsl:template>
<xsl:template match="*[starts-with(local-name(), 'TITEL')]" mode="nest">
<xsl:param name="level"/>
<xsl:choose>
<xsl:when test="$level = substring-after(local-name(), 'TITEL')">
<xsl:element name="TITEL{$level}">
<xsl:apply-templates select="."/>
<xsl:apply-templates select="following-sibling::*[1][not(starts-with(local-name(), concat('TITEL', $level)))]" mode="nest">
<xsl:with-param name="level" select="$level"/>
</xsl:apply-templates>
</xsl:element>
<xsl:apply-templates select="following-sibling::*[starts-with(local-name(), concat('TITEL', $level))][1]" mode="nest">
<xsl:with-param name="level" select="$level"/>
</xsl:apply-templates>
</xsl:when>
<xsl:otherwise>
<xsl:apply-templates select="." mode="nest">
<xsl:with-param name="level" select="$level + 1"/>
</xsl:apply-templates>
</xsl:otherwise>
</xsl:choose>
</xsl:template>
<xsl:template match="*[not(starts-with(local-name(), 'TITEL'))]" mode="nest">
<xsl:param name="level"/>
<xsl:apply-templates select="."/>
<xsl:apply-templates select="following-sibling::*[1][not(starts-with(local-name(), concat('TITEL', $level)))]" mode="nest">
<xsl:with-param name="level" select="$level"/>
</xsl:apply-templates>
</xsl:template>
<xsl:template match="#* | node()">
<xsl:copy>
<xsl:apply-templates select="#* | node()"/>
</xsl:copy>
</xsl:template>
<xsl:template match="*[starts-with(local-name(), 'TITEL')]">
<TITEL>
<xsl:apply-templates select="#* | node()"/>
</TITEL>
</xsl:template>
</xsl:stylesheet>