While it is possible to represent immensely complex structures using topic maps, the basic concepts of the model Topics, Associations, and Occurrences (TAO) are easily grasped. This paper provides a non-technical introduction to these and other concepts (the IFS and BUTS of topic maps), relating them to things that are familiar to all of us from the realms of publishing and information management, and attempting to convey some idea of the uses to which topic maps will be put in the future.
The original version of this paper was published in June 2000 and thus predates the development of XTM (XML Topic Maps). The purpose of XTM was to adapt the topic map standard (ISO 13250) for use with XML and the Web. XTM provides an alternative, XML-based syntax for expressing topic maps and also clarifies certain concepts, especially those relating to subject identity.
Since this paper deliberately avoids syntactical issues, the fact that there are now two standard interchange syntaxes for topic maps (HyTM and XTM) is not a problem. However, doing justice to the clarification of concepts would require a substantial reworking of the paper. While this updated version includes certain minor amendments to reflect changes due to XTM, readers are advised to consult [XTM 1.0] to get the full picture, paying particular attention to the notion of subject indicators, and the distinction between addressable and non-addressable subjects.
If the concepts described in this paper turn you on, look for pointers to further reading at [Ontopia 2002]. To see topic maps in action, try out the online demo of Ontopia's Omnigator, a generic topic map browser. If you find that interesting, download the free version of the Omnigator and try it with your own topic maps.
Someone once said that "a book without an index is like a country without a map".
However interesting and worthwhile the experience of driving from A to B without a map might be in its own right, there can be no doubt that when the goal is to arrive at one's destination as quickly as possible (or at least without undue delay), some kind of a map is indispensable.
Similarly, if you are looking for a particular piece of information in a book (as opposed to enjoying the experience of reading it from cover to cover), a good index is an immense asset. The traditional back-of-book index can be likened to a carefully researched and hand-crafted map, and the task of the indexer, as Larry Bonura puts it [Bonura 1994], "to chart[ing] the topics of the document and [presenting] a concise and accurate map for readers."
In Troilus and Cressida Shakespeare used a different metaphor:
And in such indexes (although small pricks
To their subsequent volumes) there is seen
The baby figure of the giant mass
Of things to come at large
but also here there is the same sense of the index replicating, in miniature, the structures of its subject, in order to provide a more manageable view of the whole.
Perhaps it isn't surprising that Shakespeare chose not to use the map metaphor. After all, the art of cartography was still in its infancy in his time ... and so too were communications. Today the situation is quite different, the sheer speed of modern communications makes accurate and advanced mapping techniques of major importance. One answer to this problem in the realm of transportation is the GPS (Global Positioning System) . The answer in the realm of publishing and information management is the new international standard, Topic Maps [ISO 13250].
Up until now there has been no equivalent of the...