This is a feature often requested in XML Schema called 
"cooccurrence constraints". It can't be done in XML Schema 1.0, unless you are 
prepared to change your <type> element into an xsi:type attribute. It will 
be possible in XML Schema 1.1, but that's still in the 
future.
 
Michael Kay
http://www.saxonica.com/
 


  
  
  From: Azariah Jeyakumar 
  [mailto:ajeyakumar@t...] 
Sent: 10 August 2007 
  22:22
To: xml-dev@l...
Subject: [xml-dev] XML 
  Schema and the Unique Particle Attribution (UPA) rule


  
  
  Hi,<o:p></o:p>
  <o:p> </o:p>
  I would like to create an XML 
  Schema for the content model like:<o:p></o:p>
  <o:p> </o:p>
  <M><o:p></o:p>
    
  <type>type1</type><o:p></o:p>
    <… several elements 
  specific to type1 …><o:p></o:p>
  </M><o:p></o:p>
  <o:p> </o:p>
  <M><o:p></o:p>
    
  <type>type2</type><o:p></o:p>
    <… several elements 
  specific to type2 …><o:p></o:p>
  </M><o:p></o:p>
  <o:p> </o:p>
  Etc<o:p></o:p>
  <o:p> </o:p>
  I was playing with a XML Schema 
  like:<o:p></o:p>
  <o:p> </o:p>
    <xs:complexType 
  name="upa_test"><o:p></o:p>
      
  <xs:choice><o:p></o:p>
        
  <xs:sequence><o:p></o:p>
          
  <xs:element name="type" type="xs:string" fixed="type1" 
  /><o:p></o:p>
          
  <xs:element name="B" type="xs:string"/><o:p></o:p>
        
  </xs:sequence><o:p></o:p>
        
  <xs:sequence><o:p></o:p>
          
  <xs:element name="type" type="xs:string" fixed="type2" 
  /><o:p></o:p>
          
  <xs:element name="C" type="xs:string"/><o:p></o:p>
        
  </xs:sequence><o:p></o:p>
      
  </xs:choice><o:p></o:p>
    
  </xs:complexType><o:p></o:p>
  <o:p> </o:p>
  But the processor I am using 
  rejects this Schema saying it violates the UPA rule. Shouldn’t the processor 
  be able to uniquely determine the particle based on the element’s type and/or 
  value? Can someone suggest an alternate XML Schema that would not violate the 
  UPA rule?<o:p></o:p>
  <o:p> </o:p>
  Changing the content model to 
  introduce an intermediate level for <type1>, <type2>, etc would 
  work, but I can’t make this change as it would break backward 
  compatibility.<o:p></o:p>
  <o:p> </o:p>
  Thanks<o:p></o:p>
  Azariah<o:p></o:p>
  <o:p> </o:p>