xsd unique identity constraint (parent and child)

[Daniel Bittner]

Fellow ranchers,

I'm trying to develop an xsd that describes java classes and their member fields. The xml content files that use this xsd will be created by other development teams, and I want to use features of xml schema to ensure that their content makes sense. In specific, a class should only be defined once, and a field should only be defined once per class.

I was able to specify classname as a key, but I am having trouble writing the xpath expressions to enforce the uniqueness of a field relative to its containing class element.

Does anyone know or have any ideas about how to do this?

Below are simplified xsd and xml for this problem.

<?xml version="1.0" encoding="UTF-8"?>
 
<xsd:schema
    xmlns:xsd="http://www.w3.org/2001/XMLSchema"
    targetNamespace="http://xml.netbeans.org/schema/sample"
    xmlns:tns="http://xml.netbeans.org/schema/sample"
    elementFormDefault="qualified">
    
    <xsd:complexType name="class-type">
        <xsd:sequence>
            <xsd:element name="field" type="tns:field-type" minOccurs="0" maxOccurs="unbounded"/>
        </xsd:sequence>
        <xsd:attribute name="classname" type="xsd:string"/>
    </xsd:complexType>
    
    <xsd:complexType name="field-type">
        <xsd:attribute name="fieldname" type="xsd:string"/>
    </xsd:complexType>
    
    <xsd:complexType name="class-list-type">
        <xsd:sequence>
            <xsd:element name="class" type="tns:class-type" minOccurs="0" maxOccurs="unbounded"/>
        </xsd:sequence>
    </xsd:complexType>
    
    <xsd:element name="class-list" type="tns:class-list-type">
        <xsd:key name="pk_classname">
            <xsd:selector xpath="tns:class"/>
            <xsd:field xpath="@classname"/>
        </xsd:key>
    </xsd:element>
</xsd:schema>

<?xml version="1.0" encoding="UTF-8"?>
 
<ns1:class-list
    xmlns:xsi='http://www.w3.org/2001/XMLSchema-instance'
    xmlns:ns1='http://xml.netbeans.org/schema/sample'
    xsi:schemaLocation='http://xml.netbeans.org/schema/sample sample.xsd'>
    
    <ns1:class classname="Class1">
        <ns1:field fieldname="x"/>
        <ns1:field fieldname="y"/>
    </ns1:class>
    
    <ns1:class classname="Class2">        
        <ns1:field fieldname="y"/>
        <ns1:field fieldname="z"/>
    </ns1:class>
    
</ns1:class-list>