Getting Topical

December 20, 2000

Simon St. Laurent

The rapid rise to prominence of Topic Maps was one of the notable features of 2000. Discussed in only a few sessions at XML'99 as an SGML-based standard (ISO 13250:2000), Topic Maps were all over the conference at XML 2000. Members of the XML Topic Maps (XTM) authoring group announced the release of core deliverables, kicking off the show with some tangible progress, while sessions, conversations, and expo floor booths all discussed the virtues of this up-and-coming application of XML.

What are XML Topic Maps?

Topic Maps provide a set of structures developers can populate with information about information -- metadata, to put it more concisely. Armed with such a map, both humans and computers can locate information by navigation among labels with well-understood relationships, rather than hoping for a successful keyword search. Topic Maps are similar to hypertext (and XLink) but operate at a level of abstraction above documents. Instead of searching for information by navigating links between documents, Topic Map users navigate links in a map, which then links to the information in documents.

Topic Maps provide flexible navigation among information items. Unlike classic indexing sites like Yahoo! or approaches like Gopher, Topic Maps uses a more hypertext-like approach: topics can have various relationships with many other topics, without any necessary conception of a hierarchical tree structure. It is possible to build topic trees using Topic Maps, but it isn't required. Instead, a "multidimensional topic space" is the model, allowing topics to connect among themselves and to information resources freely.

While Topic Maps can seem arcane, for the most part they represent a model most people are familiar with in reference works, though substantially enriched. While ordinary hypertext is like reading an encyclopedia and moving from article to article when an interesting keyword appears in the text, working with a topic map is like browsing a thesaurus and moving along the related words. When you've found the right word, you can connect to a resource that tells you much more about that word. You might have found the same information browsing an encyclopedia, but a thesaurus is often a more efficient way to navigate relationships, providing structured descriptions rather than large quantities of textual context.

Work on creating such tools in markup has been proceeding for a long time as part of HyTime SGML activity, culminating in the publication of ISO 13250:2000, Topic Maps: Information Technology -- Document Description and Markup Languages. A core group of developers, including several of the editors of the ISO specification, wanted to create an XML version of Topic Maps to bring this technology to the rapidly-growing XML community.

The Process

XML Topic Maps (XTM) launched from a meeting at last year's XML '99 conference in Philadelphia, attracting around 30 attendees after most conference-goers had moved from conference activity to dinner conversation. Those in attendance agreed that an XML version of Topic Maps was a desirable thing and decided to move toward the creation of an organization to support that development. became the new home for XML Topic Maps development, "an independent consortium of parties interested in developing the applicability of the Topic Maps Paradigm to the World Wide Web, by leveraging the XML family of specifications as required." IDEAlliance acts as the host organization, continuing a role it has played since 1993, but participants do not have to be IDEAlliance or GCA members.

Work on the Topic Maps specifications, per its charter, has taken place in public view, on the XTM-WG mailing list, hosted by eGroups. A file repository holds additional information, like use cases, meeting agendas, and minutes of face-to-face meetings. The public has read access to working documents, while members of the authoring group form the core group building the specification. Joining the authoring group requires a two-thirds vote of its current membership.

Along the way, the scope of the conversion from ISO 13250:2000 to XTM grew. "It did not happen at all the way we planned -- which is normal, because it's always like that," said Michel Biezunski of Infoloom, one of the Editors of the XTM 1.0 specification. "The thing that we did was we have the same model. Instead of just simplifying it, we discovered that many things in the model were implicit, and we had to make that clear and explicit, which was a lot of work."

The work proved to be immense, with the group dividing work among a Use Case subgroup, a Conceptual Model subgroup, and an Interchange Syntax subgroup. The need for a processing model emerged as well. Steven Newcomb, Editor of the XTM 1.0 specification, described the trial and the excitement of separating this work and uniting it into a specification: "Conceptual model group and syntax groups worked separately. The sangfroid of this group must really be admired, because we didn't know if these would fit together until the Dallas meeting."

Newcomb acknowledged the stress of the process: "Everyone worked well beyond rated capacity, and there was considerable personal sacrifice and hardship involved in getting the thing published, even in its present, only-partially-finished condition." The results, however, seem to justify that cost, as Newcomb notes:"Our interchange syntax is tuned to an explicit conceptual model, and we also provided a processing model which expresses exactly how you take a syntactic instance and turn into something that's ready to roll, ready to use."

Biezunski also noted "a lot of passion... we have had an extraordinary group -- an unexpected number of bright people, all having their personal ideas about how things should be done. We have had some very animated discussions." Murray Altheim of Sun Microsystems, an Associate Editor of the XTM 1.0 spec, described "14 hours of teleconferences in three weeks -- 20 hour a day work sometimes. A lot of time and energy. It's been an amazing process."

Topic Maps and RDF

While Topic Maps and the Resource Description Framework (RDF) appear to have some overlap -- they both describe metadata using flexible structures -- they also appear to be getting along at present. While the Extreme Markup Languages 2000 conference this past August was billed to some extent as a confrontation, it ended up as a rapprochement, something encouraged by the keynote speaker, C. Michael Sperberg-McQueen. Both groups have since spent time in conference calls and other meetings, working toward a more common purpose.

Members of both communities took pains to emphasize their cooperative and complementary nature, with Steven Newcomb noting "RDF's gem of a conceptual model." The W3C's Ralph Swick, one of the editors of RDF, attended (and was lauded at) the Topic Maps Developer Day. A number of speakers and other participants at the conference echoed the hope that six months might be all it would take to bring the two specifications into interoperability. While neither side seems inclined to abandon its projects and goals in favor of the other, accommodation of each other's models seems high on the agenda.

The Announcement

The Topic Maps highlight of the recent XML 2000 conference was Monday's announcement of the core deliverables, along with drafts of the 1.0 specification and processing model. During XML Topic Maps day, the members of the XTM Authoring Group presented introductions to Topic Maps, described how XML Topic Maps enriched the ISO 13250:2000 standard on which they are based, and congratulated themselves for having made it through an arduous but ultimately rewarding process.

The editors of the specification, tired but happy, gave attendees a brief tour of the specification, making clear the distinction between the Core Deliverables, which are fixed, and the XTM 1.0 specification as a whole, which is still in development. The Processing Model is substantially complete, but still subject to review.

Sam Hunting, of EComXML, pointed out that developers could take multiple approaches to learning about Topic Maps from the specification: "If you're a DTD geek, you can start with the DTD. If you're a UML or Java person, you can start with the conceptual model. If you think in angle brackets, you'll want to start with the examples."

The excitement of the Authoring Group was obvious, as members took the stage to describe where they'd come from and where they felt XTM was going. Members of competing companies seemed happy to share the stage, all enjoying the spotlight of having produced an agreeable specification under the terms they had decided themselves. Eric Freese caught some of the excitement when he claimed that "Whoever said standards work wasn't fun didn't know what they were talking about."

Topic Maps moving up the conference circuit

Topic Maps have been on the rise at XML conferences for the past year, moving from XML '99's Nocturne and a few presentations. A larger presence at XML Europe followed (as Liora Alschuler previously reported on, and a peaceful 'showdown' with RDF in Montreal at the Extreme Markup Languages 2000.

XML 2000 marked a coming of age for Topic Maps. Starting the conference with their own day of presentations, with a conference track largely dedicated to their field, and announcing the arrival of core deliverables the XML Topic Maps community had come a long way. Next year, the first "main event" will be a sizable upcoming presence at the Knowledge Technologies 2001 conference in March.

Moving forward

As happy as the Topic Maps authoring group seems to be with the way it met a key delivery deadline, there's still a lot of work yet to come, on nearly all fronts: specification, marketing, and implementation. Some of that work will be done by itself, while other parts of it will be done by individuals and companies building on the work already done.

On the specification front, the next task appears to be completing the XTM 1.0 specification, filling in all of the TBD (to be determined) fields while remaining consistent with the fixed Core Deliverables and the XTM 1.0 goals. Michel Biezunski noted that "three days of meetings in Paris on the 1.0 specification" loomed, with an "RDF session to be on the agenda." Murray Altheim noted that "We have infoglut that we need to map," and some developers were talking about creating a topic map for Topic Maps itself.

While Steve Newcomb acknowledges some technical challenges ahead (like "figuring out how to allow portions of topic map graphs held in remote servers to be accessed and treated as if they were merged with other topic map graphs held in other remote servers"), he notes that "It's not yet the 'Semantic Web' in all its glory, but it's a solid start and it's already the most powerful means of sharing 'finding information'."

On the marketing side, has a marketing subgroup, currently chaired by Jason Markos of empolis, and offers sponsoring memberships and logo use. Markos notes that "the team recognized that a standard not only needs to be 'intellectually' good to succeed, but it will also need to be adopted -- this takes marketing."

Organizations using Topic Maps are selling them vigorously, however, and largely into business fields where navigating huge quantities of information is a common and difficult problem. A number of companies are currently focusing on Topic Maps, notably XTM sponsors empolis, Infoloom, Mondeca, and Ontopia, while many of the participants offer consulting services. Markos points out that "All four of the founding sponsors are doing business, actually making money, from Topic Maps. That in itself is a significant step forward."

XTM provides a specification and a processing model but not an implementation. Other organizations, generally companies and consultants, are creating and integrating Topic Map engines, editors, and processors for creating, storing, and manipulating Topic Maps, as well as tools for navigating and exploring maps. Organizations which want to use these tools will need training and consulting services to make the best use of them as well.

Topic Maps seems to have a lot of momentum, much of it rooted in the working group's continuing enthusiasm and its members willingness to develop implementations. Steven Newcomb noted that "It's okay for people who share an interest to get together and make a standard. It's a radical thing to say."