An irritant with keyref in XML Schema (fix)

It turns out that my problem was just an issue with scoping, and was probably made more complex-looking because of the use of refs and groups within the XSD I was given.

To fix the issue raised here, I had to get the <unique>  and <keyref>  nodes at the same scope.  I’m not sure yet if they have to be in the same document or not, but that’s how I did it.  There was some minor tweaking needed in the XPath for the unique node, but it was trivial.  The result, with both nodes in the root <element>  definition:

<xs:unique name="uniqueParameterName">
  <xs:selector xpath=".//item/parameter"/>
  <xs:field xpath="name"/>
<xs:keyref name="engineParameterRef" refer="uniqueParameterName">
  <xs:selector xpath="./engine"/>
  <xs:field xpath="parameter_name"/>

And now it validates if there are engine nodes with matching item parameters, and it validates if there are no engine nodes and no item nodes.

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