Topic Maps: From Information to Discourse Architecture

Topic Maps is a standards-based technology and model for organizing and integrating digital information in a range of applications and domains. Drawing on notions adapted from current discourse theory, this article focuses on the communicative, or explanatory, potential of topic maps. It is demonstrated that topic maps may be structured in ways that are “text-like” in character and, therefore, conducive to more expository or discursive forms of machine-readable information architecture. More specifically, it is exemplified how a certain measure of “texture”, i.e. textual cohesion and coherence, may be built into topic maps. Further, it is argued that the capability to represent and organize discourse structure may prove useful, if not essential, in systems and services associated with the emerging Socio-Semantic Web. As an example, it is illustrated how topic maps may be put to use within an area such as distributed semantic microblogging1. TOPIC MAPS AS INFORMATION ARCHITECTURE Topic Maps (in upper case) is a standards-based technology for connecting knowledge structures to information resources. Topic maps (in lower case) are concrete manifestations of this technology: digital collections of topics representing and connecting things, or “subjects”, in some universe of discourse (persons, events, concepts, documents, web pages, etc.). Topic maps are often described as a kind of superimposed semantic metadata layer for indexing (often dispersed and heterogeneous) information resources but topic maps may in fact realize a number of organization schemes ranging from simple taxonomies to semantically rich ontologies (Garshol, 2004). Topic maps are supported by various query languages, exchange formats and development and publication tools and are increasingly used in web sites, knowledge portals, content management systems and social bookmarking services (Lachica & Karabeg 2008, Garshol 2008, and Pepper 2010). Examples of real world applications are the city of Bergen’s portal (https://www.bergen.kommune.no/), VIMU, a website on Danish-German border history (http://www.vimu.info) or fuzzzy.com, a social bookmarking site (http://www.fuzzzy.com/). 1 I am greatly indebted to the anonymous reviewers for their valuable comments on this article. JOURNALOFIA.ORG | ISSN 1903-7260 5 LARS JOHNSEN | TOPIC MAPS: FROM INFORMATION TO DISCOURSE ARCHITECTURE In a topic map, topics may be given one or more names; they may be categorized in types, subtypes and instances and they may be connected to internal content (information within the topic map itself descriptions, data values, etc.) as well as external content (resources outside the topic map itself web pages, files, etc.). Topics may be related in typed associations in which they are assigned semantic roles and they may be linked to external descriptors, for instance Wikipedia entries, to make their meaning, or subject identity, more transparent. These external descriptors, also known as subject indicators, are accessed through subject identifiers, usually URL’s. Subject identifiers are central to the Topic Maps paradigm because they facilitate the merging of topics sharing one or more subject identifiers, and hence the integration of disparate topic maps. The use of stable, publicly available subject indicators and identifiers, so-called PSI’s and PSID’s, is strongly recommended in the Topic Maps community as the key to more reliable data integration and knowledge federation (Pepper, 2003). For example, in a knowledge portal of ancient Roman history, the subjects of “Brutus” and “Caesar” might be introduced as topics, named and categorized as “Roman” (in itself a topic) using the “is-a” association. The topic of “Roman” might in turn be defined to be a subtype of “person” by means of the “a-kind-of” association. Some internal content could be attached to the topic of Brutus to describe him, for instance the years of his birth and death. A pointer to a picture of him, i.e. content external to the topic map, might also be provided to enrich the description. And to indicate more precisely which Brutus is being referred to, his full name “Marcus Junius Brutus” could be given along with a subject identifier pointing to his entry in Wikipedia. Finally, an association might state that Brutus killed Caesar with a dagger. In this association Caesar would play the semantic role of “victim”, Brutus the role of “murderer” and the dagger the role of “instrument”. In such a history portal, the information structure would be centered around domain entities or so-called non-addressable subjects (Brutus, Caesar, being Roman, dagger, etc.). However, topic maps may also be employed to create information architecture comprising digital content items, or addressable subjects. For example, a topic map might be employed in an e-learning system to organize distributed learning resources on the web. Here the individual topics would represent digital “learning objects” like articles, video lectures or slides. The topics would, therefore, not have subject identifiers but subject locators, pointers to the actual content items, in effect their web addresses. Linking of topics representing both addressable and non-addressable subjects is also possible in a topic map. This may, for instance, be the case in a topic maps-based bookmarking service where web users can collectively store bookmarks and links. Users and bookmarks would constitute non-addressable subjects, while the actual web content items being referred to would be addressable ones. Generally, topic maps used for information architecture may be visualized in the following way: