XSD Key/KeyRef and how to reference

We use XML to define a model which we later use to generate code. The file looks something like this:

<def xmlns="http://tempuri.org/schema.xsd" xmlns:xsi="http://tempuri.org/schema.xsd"&开发者_StackOverflow中文版gt;
  <ns xmlns=""  name="asd">
    <alias name="NicknameType" ref="String" />
    <alias name="SomethingType" ref="o3" />

    <obj1 name="o1">
       <element name="Nick" ref="NicknameType" />
    </obj1 >

    <obj2 name="o2">
        <action name="a1">
            <attribute name="TheObject1" ref="o1" />
        </action>
    </obj2 >

    <obj3 name="o3">
        <element name="SomeText" ref="int32" />
    </obj3 >
  </ns>
</def>

What I would really like to enforce is that the ref-attribute of any tag matches the name tag of either an alias-tag, an obj1-tag or an obj2 tag or some predefined values such as String or int32. I already defined the general structure that the file has to have in XSD. Is what I would like to achieve even possible with XSD?

Thanks

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It's possible in XSD 1.1, using assertions, but not in XSD 1.0.

The latest releases of the schema processors in Saxon and Xerces both have support for assertions.