XML schema - key/keyref and inheritance

[peterpeter]

Hi.

There is a XML schema problem that I have with key/keyref:

I have two complex (A and B) types which both inherit from a common base typ (Base). A refers B using a xs:IDREF element named Ref_to_A. Both are allowed to be instantiated under the root element by declaring an element of the base class.

I want to have type safety for the reference by using key/keyref. There should be a key definition for the @key attribute of type A and a keyref definition between this key and the Ref_to_A element of type B.

But there's a problem: The XPath expressions in key/keyref do not allow to contain tests like [@type='A']. How can I reach the instance element of type A or B with my XPAth? Or is there another solution?

Thanks for helpful answers...

Peter

Here is the schema:

<?xml version="1.0" encoding="UTF-8"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"> <xs:element name="Root" type="Root"/> <xs:complexType name="Root"> <xs:sequence> <xs:element name="Base" type="Base" minOccurs="0" maxOccurs="unbounded"/> </xs:sequence> </xs:complexType> <xs:complexType name="Base" abstract="true"> <xs:attribute name="key" type="xs:ID" use="required"/> </xs:complexType> <xs:complexType name="A"> <xs:complexContent> <xs:extension base="Base"/> </xs:complexContent> </xs:complexType> <xs:complexType name="B"> <xs:complexContent> <xs:extension base="Base"> <xs:sequence> <xs:element name="Ref_to_A" type="xs:IDREF"/> </xs:sequence> </xs:extension> </xs:complexContent> </xs:complexType> </xs:schema>

And here is an instance example:

<?xml version="1.0" encoding="UTF-8"?>
<Root xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="test.xsd"> <Base xsi:type="A" key="key1"/> <Base xsi:type="B" key="key2"> <Ref_to_A>key1</Ref_to_A> </Base> </Root>

I planned these key/keyref to be within my instance element declaration of the Root:

<xs:element name="Root" type="Root">
<xs:key name="InvalidKey">
<xs:selector xpath="Base[@type="A"]"/>
<xs:field xpath="@key"/>
</xs:key>
<xs:keyref name="InvalidKeyref" refer="InvalidKey">
<xs:selector xpath="Base[@type="B"]/Ref_to_A"/>
<xs:field xpath="."/>
</xs:keyref>
</xs:element>