RDF and Topic Maps

Extreme Markup 2000 was held August 15-18 in Montreal.  Extreme is a new, highly technical conference, concentrating on the evolving abstractions that underlie modern information management solutions, how those abstractions enhance human productivity, and how they are being applied.  Abstract and concrete information models, systems built on them, software to exploit them, SGML, XML, XSL, XLink, schemas, Topic Maps, RDF, query languages, and other markup-related topics fell within scope for this conference.

Perhaps the most exciting event of the conference was the face-off between two knowledge technologies -- RDF and Topic Maps.  Presented by conference chair, Steve Newcomb, Eric Freese, (Isogen/Datachannel) represented ISO Topic Maps, while Eric Miller (OCLC) represented RDF.  Coming to the stage in their "boxing robes" to the roar of the crowd, the face-off between the two "Erics" began!  Each opponent first provided a brief overview of their standard of choice.

ISO Topic Maps

Eric Freese began by inciting the crowd with his slogan "Anything RDF can do, Topic Maps can do better!"  Eric then presented a general overview to Topic Maps.  Topic Maps, as presented by Eric Freese, is among the newest ISO standards, ISO 13250.  Core to this standard is the concept of a topic which is at one time both a concept and the occurrences of that concept within a set of resources.  Eric then described the concepts of topic types, topic associations, occurrence roles, themes, scopes and facets.  Eric informed the audience that while the official syntax for ISO Topic Maps is SGML, a new working group, TopicMaps.org, hosted by IDEAlliance, is working to create a specification for XML syntax (XTM) and further optimize Topic Maps for use on the Web.

Resource Definition Framework (RDF)

Eric Miller began by stating that his examination of Topic Maps shows a great similarity to RDF.  RDF is a W3C recommendation.  According to Eric, a resource is anything that can be identified.  RDF has a data model that enables a web of named relationships connecting all identified relationships.  Currently RDF has an XML representation.  RDF has structural constraints than govern the encoding, exchange and processing of resource metadata.  An RDF statement consists of two resources connected by a property.  The basis of an RDF schema is to enable resource description and enables that definition and sharing of vocabularies.  RDF is designed to support basic semantic integrity constraints.

RDF Vs. ISO Topic Maps

After initial overviews of RDF and ISO Topic Maps, both "Erics" moved to find what relationship there was between the two.  Of keen interest to the audience was the determination as to whether these are competing standards, or whether RDF and Topic Maps could somehow work together.

According to Miller, a topic is very much like a resource.  Both topics and resources have associations and relationship constraints.  Miller also stated that RDF has the goal of putting a resource in context with other resources.  Topic Maps does this as well.  And, as Miller and Freese will both agree, the specifications are equally difficult to read!

Miller provided the following equivalency table:

* reification is the means for context validation in RDF

Conclusion

In conclusion, both "Erics" agreed that there are many similarities between RDF and Topic Maps.  The goals are similar, but RDF was specifically developed for the Web, while Topic Maps have many scopes of application.  Michel Biezunski provided his insight that the relationship between the two is much like the relationship between Physics and Chemistry.  While there is some overlap, Physics focuses on the "atom" while Chemistry focuses on the combination of atoms into molecules.  Biezunski, co-editor of ISO 13250 and a co-chair of the XTM activity, believes that the focus of RDF is much like Physics while Topic Maps is more like Chemistry.

Benefits to be gained from an industry understanding of how RDF and TM relate and work together were identified:

• Clarity in the market

• Use of similar tools for RDF and Topic Maps

• Identification of common inference roles

• Common query language

A final observation is that the syntaxes for the serialization of the RDF model are lacking and that perhaps the fit for RDF and Topic Maps is that Topic Maps may well become a new syntax for RDF serialization.  Whether you are a fan of Topic Maps or RDF, the good news is that greater understanding was gained between these two groups and talks will continue.  You can follow the discussion taking place in the XTM-WG list serv by signing up at http://www.egroups.com.

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