xmlhack: RDF and Topic Maps, so similar and so different!

Graham Moore presented "RDF and Topic Maps: An Exercise in Convergence" (pdf), a demonstration that Topic Maps can be modeled in RDF and RDF can be modeled as Topic Maps, along with a proposal to define a metadata-based mapping to transition between the two languages.

After comparing the data models of the two standards, Moore showed that they are both expressive and generic enough for Topic Maps to model RDF and vice-versa.

This simple layered modeling fails to capture the commonalities between the semantics of RDF and Topic Maps and would not allow querying Topic Maps as triples or RDF triples as topics and associations. Moore would like to define a bridge between the two languages that would keep them at the same level.

The atomic models are quite different. RDF triples are directional identified arcs between two resources, while the most similar Topic Map construct is an association (bi-directional and multi-qualified) between two topics.

To build his bridge, Moore proposed adding some objects to the Topic Map data model that could be used for the mapping.

He also noted that in practice some Topic Map software are already presenting topic associations to the users in a simplified way that is similar to RDF triples and that this addition could be beneficial for the Topic Map data model.

This proposal is still a work in progress. The mappings of important Topic Map notions such as scopes have not been studied yet and some attendees expressed doubts about the scalability of this mapping to complex topic associations, but this proposal shows a way that seems worth investigating and could be supported by software vendors whose products could support both XTM and RDF as serialization formats.

Concluding the session, Steve Newcomb announced three more papers on Topic Maps and RDF convergence at the August Extreme Markup Language 2001 conference.