Why isn in the model?
As the element type name says it is really just a reference to a topic; in the data model this turns into a topic item in the value of some property. There is no information in the reference itself that is relevant to the parsed topic map, and so the reference is replaced by the topic item itself (in the model; an implementation will almost certainly have a reference of some sort). Again, the XTM 1.1 specification has the details.
