How can I overload an element type in a xml schema file?

We are using xmlbeans to generate java source code base on the schema file, and I'm trying to achieve a scenario where two classes which only differ in one aspect share the same interface, in order to avoid repeating code:

public interface Request extends Message {
  RequestType getType();
  // this would be an interface
  RequestData data;
  Authentication getAuth();
  // etc...
}

public interface RequestOne() extends Request {
   RequestOneData data;
}

public interface RequestTwo() extends Request {
   RequestTwoData data;
}

The problem is, I don't know how to achieve this my xml schema, as the data element is required to be between RequestType and Authentication, as such:

<request-one>
    <type>...</type>
    <data>
       <1>a</1>
       <2>b</2>
    </data>
    <auth>...</auth>
</request-one>

<request-two>
    <type>...</type>
    <data>
       <1>a</1>
       <2>b</2>
       <3>c</3>
    </data>
    <auth>...</auth>
</request-two>

The problem is, I can't use <xsd:extension base="tns:Request"> in RequestA and RequestB, as changing the type of element data is invalid. Is there another way I can achieve this with an xml schema and xmlbeans?