Dissertation abstract

Information retrieval can be defined as the extraction of specific information out of a great number of stored information items. Information retrieval systems, used for the retrieval of documents, try to answer more or less precise questions about interesting topics with a number of suitable documents or references to documents. Such systems should contain 'knowledge' about the meaning of questions, about the content of the stored information and the particular user's needs for information.Knowledge-bases systems claim to be able to store knowledge an draw conclusions from it. The goal of this thesis is to investigate the use of knowledge-based methods and technologies for information retrieval. A knowledge-based information retrieval system should represent its Information Structures, as well as knowledge in a common knowledge representation formalism. The retrieval process of the system should employ the inferential methods of the used knowledge representation formalism.A subset of first order logic is chosen for this thesis to represent knowledge. Specially designed retrieval rules represent knowledge for the purpose of retrieval. Retrieval rules capture knowledge about the user's vocabulary, his working domain and his way to perform the retrieval of documents. The problem of recall and precision of the answers of an information retrieval system is approached by an explicit representation of control knowledge.A theoretical model of a knowledge-based information retrieval system developed in this thesis specifies the requirements and properties, of such a system. In particular a novel term-similarity function could be defined. Properties like completeness and termination could be derived and boundaries for the amount of overhead of false control strategies could be investigated.The proposed model is implemented in a prototype of a knowledge-based information retrieval system, called KIR. KIR is a single-user system for personal document- and knowledge retrieval running on computer workstations. It is implemented using Prolog and Modula-2.