You have a document that encodes information using child elements, and you would like to use attributes instead.

As with Recipe 6.1, you can use the overriding copy idiom. However, when transforming elements to attributes, you must selectively determine where the transformation will be applied. This is because the idea of transforming all elements to attributes is nonsensical. The following stylesheet reverses the attribute-to-element transformation we performed in Recipe 6.1:

<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
   
<xsl:import href="copy.xslt"/>
   
<xsl:output method="xml" version="1.0" encoding="UTF-8"/>
   
<xsl:template match="person">
  <xsl:copy>
    <xsl:for-each select="*">
      <xsl:attribute name="{local-name(.)}">
        <xsl:value-of select="."/>
      </xsl:attribute>  
    </xsl:for-each>
  </xsl:copy>
</xsl:template>
   
</xsl:stylesheet>

Converting from elements to attributes is not always as straightforward as transforming in the opposite direction. If the elements being converted to attributes have attributes themselves, you must decide what will become of them. In the preceding solution, they would be lost. Another alternative would be to promote them to the new parent:

<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
   
<xsl:import href="copy.xslt"/>
   
<xsl:output method="xml" version="1.0" encoding="UTF-8"/>
   
<xsl:template match="person">
  <xsl:copy>
    <xsl:for-each select="*">
      <xsl:attribute name="{local-name(.)}">
        <xsl:value-of select="."/>
      </xsl:attribute>  
      <xsl:copy-of select="@*"/>
    </xsl:for-each>
  </xsl:copy>
</xsl:template>
   
</xsl:stylesheet>

However, this works only if all the attributes names in question are unique. If this is not the case, you will have to rename attributes, perhaps as follows:

<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
   
<xsl:import href="copy.xslt"/>
   
<xsl:output method="xml" version="1.0" encoding="UTF-8"/>
   
<xsl:template match="person">
  <xsl:copy>
    <xsl:for-each select="*">
      <xsl:attribute name="{local-name(.)}">
        <xsl:value-of select="."/>
      </xsl:attribute>  
      <xsl:variable name="elem-name" select="local-name(.)"/>
               <xsl:for-each select="@*">
               <xsl:attribute name="{concat($elem-name,'-',local-name(.))}">
               <xsl:value-of select="."/>
               </xsl:attribute>  
               </xsl:for-each>
    </xsl:for-each>
  </xsl:copy>
</xsl:template>
   
</xsl:stylesheet>

Another complication arises if the siblings elements do not have unique names, because in this case, they would clash upon becoming attributes. Another possible strategy is to create an attribute from an element only if the element does not have attributes or element children of its own, does not repeat in its parent element, and has parents without attributes:

<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
   
<xsl:import href="copy.xslt"/>
   
<xsl:output method="xml" indent="yes" version="1.0" encoding="UTF-8"/>
   
<!-- Match elements that are parents -->
<xsl:template match="*[*]">
  <xsl:choose>
    <!-- Only convert children if this element has no attributes -->
    <!-- of its own -->
    <xsl:when test="not(@*)">
      <xsl:copy>
        <!-- Convert children to attributes if the child has -->
        <!-- no children or attributes and has a unique name -->
        <!-- amoung its siblings -->
        <xsl:for-each select="*">
          <xsl:choose>
            <xsl:when test="not(*) and not(@*) and
                            not(preceding-sibling::*[name(  ) =
                                                     name(current(  ))]) 
                            and 
                            not(following-sibling::*[name(  ) = 
                                                     name(current(  ))])">
              <xsl:attribute name="{local-name(.)}">
                <xsl:value-of select="."/>
              </xsl:attribute>  
            </xsl:when>
            <xsl:otherwise>
              <xsl:apply-templates select="."/>
            </xsl:otherwise>
          </xsl:choose>
        </xsl:for-each>
      </xsl:copy>
    </xsl:when>
    <xsl:otherwise>
      <xsl:copy>
        <xsl:apply-templates/>
      </xsl:copy>
    </xsl:otherwise>
  </xsl:choose>
</xsl:template>
   
</xsl:stylesheet>