Validate dependencies using Schema/XSLT

shumba · March 19th, 2006, 09:21 AM

Suppose I have the following XML instance document.

Code:

<computer>
   <component number="78" name="chassis">
      <related-to>79</related-to>
      <related-to>80</related-to>
   </component>
   <component number="79" name="hard-disk">
      <related-to>80</related-to>
   </component>
   <component number="80" name="screen">
      <related-to>78</related-to>
   </component>
</computer>

I need to validate that every related-to text content refers to an existing number attribute i.e. all components should relate to existing components.

Now I can do this very well in my XML Schema and I have tested and it works ok. The XML Schema is as follows

Code:

<?xml version="1.0" encoding="UTF-8"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">

   <xs:element name="computer">
      <xs:complexType>
         <xs:sequence>
            <xs:element name="component" type="partType" maxOccurs="unbounded"/>
         </xs:sequence>
      </xs:complexType>

      <xs:key name="key">
         <xs:selector xpath="component"/>
         <xs:field xpath="@number"/>
      </xs:key>

      <xs:keyref name="numKey" refer="key">
         <xs:selector xpath="component/related-to"/>
         <xs:field xpath="."/>
      </xs:keyref>
   </xs:element>

   <xs:complexType name="partType">
      <xs:sequence>
         <xs:element name="related-to" type="xs:positiveInteger" maxOccurs="unbounded"/>
      </xs:sequence>
      <xs:attribute name="name" type="xs:token" use="required"/>
      <xs:attribute name="number" type="xs:positiveInteger" use="required"/>
   </xs:complexType>
</xs:schema>

Now I need to write an XSL Stylesheet to check the same dependencies that the XML Schema does. This is because the server side uses the Schema and on the client side, a stylesheet validation is required. Not particularly sure why can not use Schema on both client/server.

Basically, I need to go through every component and find its relate-to text contents. Then I need to check to make sure this actually relates to some @number attribute in any other component but the one I am currently looking at.

I am wondering if people can help me on what the best approach is to this. Actual XSLT code is helpful but I really need to understand on how to go about it.

I am thinking of doing this

1. creating a node set of all //related-to contents and another node set of the number attribute like //@number
2. For each element in the //related-to node set, loop through the //@number and see if I find one that matches

Basically, I want to do the equivalent of this portion of my Schema

Code:

      <xs:key name="key">
         <xs:selector xpath="component"/>
         <xs:field xpath="@number"/>
      </xs:key>

      <xs:keyref name="numKey" refer="key">
         <xs:selector xpath="component/related-to"/>
         <xs:field xpath="."/>
      </xs:keyref>

Thanks
Shumba

mhkay · March 19th, 2006, 01:53 PM

First define a key that finds a component given its number:

<xsl:key name="k" match="component" use="@number"/>

Now find all the related-to elements for which there is no key match:

<xsl:variable name="unmatched" select="//related-to[not(key('k', .)]"/>

Now report errors in respect of any node in $unmatched.

Michael Kay
http://www.saxonica.com/
Author, XSLT Programmer's Reference and XPath 2.0 Programmer's Reference

shumba · March 19th, 2006, 02:17 PM

I've only recently started studying XSLT and will need to read up on using the "key" matching. I will see if I can try to understand your advice after that. As at now, I am not sure how to fit your suggestions into my XSlT stylesheet such that I can print out anything without dependencies.

shumba · March 22nd, 2006, 03:56 PM

ok. After doing some reading and practice, I think I have managed to do this.

I have first created a lookup "table" for all components based on their @number attribute key

Code:

   <xsl:key name="refNums" match="component" use="@number"/>

Then in my related-to template, I call a named template that I have written to resolve that the part actually exists in the lookup "table" above. I use the text content of related-to to find if the part really exists in the lookup "table" I created earlier. If it does not, I handle it according - I just printed out for testing purposes

Code:

   <xsl:template match="related-to">
         <xsl:call-template name="resolveNumber">
            <xsl:with-param name="partNum" select="."/>
         </xsl:call-template>
   </xsl:template>
   <xsl:template name="resolveNumber">
      <xsl:param name="partNum"/>
      <xsl:choose>

         <xsl:when test="key('refNums', $partNum)">

               Part number: <xsl:value-of select="$partNum"/> exists
         </xsl:when>
         <xsl:otherwise>

               Part number: <xsl:value-of select="$partNum"/> does not exists

         </xsl:otherwise>
      </xsl:choose>
   </xsl:template>

If there is a better way to do this, please advise

Thanks
Shumba

mhkay · March 22nd, 2006, 04:45 PM

Your solution is fine. Your approach is fine too: doing some reading and experimenting and then coming back to post the solution.

Michael Kay
http://www.saxonica.com/
Author, XSLT Programmer's Reference and XPath 2.0 Programmer's Reference