The Various Roles of Information Structures

Information structures represent a domain of discourse in a formal way. The objective of an information structure is to improve the process of retrieving information. The various roles information structures can play in a retrieval system are described. After discussing the role of a controlled indexing vocabulary, we focus on information structures that are aimed at helping users to formulate appropriate queries. Conventional thesauri are often used for this purpose. As an alternative we present a new information structure which we call a similarity thesaurus. In contrast to conventional thesauri, the construction and the maintenance of similarity thesauri is inexpensive and in addition, they can be improved systematically. Finally, we summarize the different aspects that should be considered when augmenting a retrieval system by an information structure.