An Approach to Dynamic Schema-Aware Decision Making?

whelanj · April 2nd, 2010, 02:37 PM

I'm trying to take a input element which is a union of types, and produce outputs of the specific type described in the union. The schema for this is as follows:

Code:

<?xml version="1.0" encoding="UTF-8"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"
           xmlns:test="http://www.example.com/test"
           targetNamespace="http://www.example.com/test">
 
  <xs:element name="root">
  <xs:complexType>
   <xs:sequence>
    <xs:element ref="test:union" maxOccurs="unbounded"/>
   </xs:sequence>
  </xs:complexType>
 </xs:element>
 
 <xs:element name="union">
  <xs:complexType>
     <xs:attribute name="type" type="xs:string"/>
     <xs:attribute name="x" type="xs:string"/>
     <xs:attribute name="y" type="xs:string"/>
     <xs:attribute name="z" type="xs:string"/>
  </xs:complexType>
 </xs:element>
 
 <xs:element name="a">
  <xs:complexType>
     <xs:attribute name="x" type="xs:string"/>
     <xs:attribute name="y" type="xs:string"/>
  </xs:complexType>
 </xs:element>
 
 <xs:element name="b">
  <xs:complexType>
     <xs:attribute name="y" type="xs:string"/>
     <xs:attribute name="z" type="xs:string"/>
     <xs:attribute ref="test:q"/>
  </xs:complexType>
 </xs:element>
 
 <xs:attribute name="q" type="xs:string"/>
 
</xs:schema>

What I want is to take an input like the following:

Code:

<?xml version="1.0" encoding="UTF-8"?>
<root xmlns:test="http://www.example.com/test"
            xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
            xsi:schemaLocation="http://www.example.com/test input.xsd">
 <union type="a" x="123" y="456" z=""/>
 <union type="b" x=""    y="456" z="789"/>
 <union type="b" x=""    y=""    z="0"/>
</root>

And produce the following:

Code:

<?xml version="1.0" encoding="UTF-8"?>
<results xmlns:xs="http://www.w3.org/2001/XMLSchema"
         xmlns:xslo="http://www.w3.org/1999/XSL/TransformAlias"
         xmlns:fn="http://www.w3.org/2005/xpath-functions"
         xmlns:test="http://www.example.com/test">
 <a xmlns="http://www.example.com/test" x="123" y="456"/>
 <b xmlns="http://www.example.com/test" y="456" z="789"/>
 <b xmlns="http://www.example.com/test" y=""    z="0"/>
</results>

I started down the path of using schema-attribute(), but I was not able to work with variables since it is [FONT='Calibri','sans-serif']determined [/font]compile-time. I also understand that it only works with top-level attribute declarations, which I do not have.

I then started working a two stage approach, where the first transformation only copied over the non-empty attributes to the output elements, and then I used a second stage schema-aware transformation to populate the missing (valid but set to 'empty string') attributes via XSD default values. The problems with this approach are that I end up losing all difference between empty-string and unset for optional attributes. I also believe that there would be run-time validation problems in using SA to populate default values if the element were missing required attributes, and this approach wouldn't cover required attributes.

All said, I might pursue the two-stage approach, but would need to greatly restrict the supported use cases. Before going down that path, I was wondering if anyone had ideas on how to this could be made to work. My best, but failed, attempt is as follows:

Code:

<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet 
  xmlns:xsl="http://www.w3.org/1999/XSL/Transform" 
  xmlns:xslo="http://www.w3.org/1999/XSL/TransformAlias"
  xmlns:fn="http://www.w3.org/2005/xpath-functions"
  xmlns:xs="http://www.w3.org/2001/XMLSchema"
  xmlns:test="http://www.example.com/test"
  version="2.0">
  <xsl:output  method="xml" indent="yes" omit-xml-declaration="no"/>
 
  <xsl:import-schema schema-location="input.xsd" namespace="http://www.example.com/test"/>
      </xsl:variable>
      <xsl:element name="{@type}" namespace="http://www.example.com/test">
         <xsl:for-each select="@*">
            <xsl:variable name="testAttr">
               <xsl:text>test:</xsl:text><xsl:value-of select="name(.)" />
            </xsl:variable>
            <xsl:if test="$testObj//schema-attribute(test:q)">
               <xsl:attribute name="{name()}">
                  <xsl:value-of select="." />
               </xsl:attribute>
            </xsl:if>
         </xsl:for-each>
         <xsl:attribute name="TheEnd">
            <xsl:value-of select="." />
         </xsl:attribute>
      </xsl:element>
 </xsl:template>
</xsl:stylesheet>

Any ideas on how to approach this? Can this not be done in straight XSL?