Topic maps rhetoric has long maintained that different domains of discourse may have different ways to identify some single subject.
Topic maps provide the means to map between those different identifications, to provide a collocation point for all the information about such a subject.
If different domains can have different ways to identify the same subject, doesn’t it stand to reason that they can also have different ways to map subject identifications from other domains?
Some of them may lack any concept of mapping to/from foreign identifications. Identifications are expressed in a given vocabulary or not at all. Other will have a variety of concepts of mapping, some broader, some narrower.
Understanding subject identifications in various domains as well as their concepts of mapping between domains, will only improve our promotion of topic maps.