XML Schema co-occurrence constraint workaround
Here's a potential workaround for the co-constraint problem in XML Schema. Given some XML: <elem type="typeA"> <typeA/> </elem> <elem type="typeB"> <typeB/> </elem> ...the problem is you can't constrain the contents of <elem> based on the value of the type attribute. You can do it though, if you add an xsi:type attribute to it to explicitly set its type: <elem type="typeA" xsi:type="elem_typeA"> <typeA/> </elem> <elem type="typeB" xsi:type="elem_typeB"> <typeB/> </elem> with suitable type definitions in the schema: <xs:complexType name="elem_typeA"> <xs:sequence> <xs:element ref="typeA"/> ... <xs:complexType name="elem_typeB"> <xs:sequence> <xs:element ref="typeB"/> ... ...and when the XML is validated the relevant definition will be used. This technique is far from ideal as it involves modifying the source, but only in a way which doesn't break it for anyone else. Given the various options for validating co-constraints, this could well be the most straightforward way (at least until 1.1 comes along). (pasted from http://ajwelch.blogspot.com/2008/06/xml-schema-co-occurrence-constraint.html) -- Andrew Welch http://andrewjwelch.com Kernow: http://kernowforsaxon.sf.net/
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