A standard for specifying arbitrary relations between objects. Has standardized machinery for distinguishing the object itself from a web site having to do with the object (i.e. RDF is a standard, and here is a webpage with the spec). Was first conceived as a way to solve the problem of indexing hyperdocuments in an extensible, mergable way.
Quoting DannyAyers: "Things might get messy using the XTM XML syntax directly, but this stuff can already be represented easily in RDF - maybe best through one of the translations of TMs to RDF schema."
- [Topic Maps, RDF, OIL, and DAML] A good paper comparing and contrasting RDF and TopicMaps (and two other formats)
- [The TAO of Topic Maps]