Hi Paul,

It is not clear if you are talking about elements with simple type or 
elements with complex type. If your elements have simple type then you 
can use an xs:union of the different identifier types.
If your elements have complex type then you can use an abstract type for 
them, thus you force the user to specify a non abstract type using 
xsi:type in the instance document.

Best Regards,
George
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George Cristian Bina
<oXygen/> XML Editor, Schema Editor and XSLT Editor/Debugger
www.---.com


Paul Spencer wrote:
> In the Election Markup Language, people may use a variety of identifiers
> depending on the type of election, country etc. The schema (XSD) therefore
> allows use of xsi:type in the instance so that the correct validation can be
> used for each identifier. I don't think that there is any way in XML Schema
> of forcing the use of the xsi:type attribute in the instance, so I am
> currently using Schematron rules to do this. Am I correct, or have I missed
> something obvious?
> 
> Before people point out that I am allowing the sender of the message to say
> what type of identifier they have, the Schematron (which changes for each
> scenario) also defines the allowed values for xsi:type. I would keep this,
> but it would be good if the schema itself enforced something as a hint to
> implementers to look at the spec and see what they need to do.
> 
> Regards
> 
> Paul Spencer
> 
> 
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