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RE: [xml-dev] How to Unique contraint


It's not valid because the field xpath is only allowed to return zero or one
node relative to the selector xpath, and in this case it would return two.
(Validation Rule: Identity-constraint Satisfied, part #3) [1].

I can't think of a way to do this with the XML you've got, but if you
changed the attributes into child elements, as in:


you could use:

    <xs:unique name="port">
      <xs:selector xpath="anElement/port|anElement/debug-port"/>
      <xs:field xpath="."/>

(You can't use anElement/@port|anElement/@debug-port in the selector because
you are not allowed to use the attribute axis in the selector.)

Hope that (sort of) helps,

Priscilla Walmsley
Author, Definitive XML Schema

[1] http://www.w3.org/TR/xmlschema-1/#cvc-identity-constraint

> -----Original Message-----
> From: Michael Kay [mailto:mike@saxonica.com] 
> Sent: Wednesday, March 21, 2007 2:11 PM
> To: smcardle@spansurf.com; xml-dev@lists.xml.org
> Subject: RE: [xml-dev] How to Unique contraint
> > 
> > Does anybody know how to do this so it looks something like 
> > the following INVALID constraint, but I hope you get the picture.
> > 
> > <xs:unique name="port">
> > 	<xs:selector xpath="anElement"/>
> > 	<xs:field xpath="@debug-port | @port"/> </xs:unique>
> > 
> What makes you think this constraint is invalid? It looks OK to me.
> Michael Kay
> http://www.saxonica.com/
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