Ontologies and Query expansion

This master thesis will explore the use of ontologies in information retrieval and in query expansion in particular. Ontologies are usually huge, hand-coded repositories of concepts and relations between them so using them in information retrieval seems to be a reasonable goal. We feel that the use of ontologies for query expansion in particular has been overlooked in contemporary literature, as the main related papers date before 2000. In this thesis we will attempt to present a query expansion method using ontologies that outperforms non-ontological query expansion methods. Note, however, that the presented approach is not purely ontological but is rather a hybrid approach as it uses non-ontological steps. We also propose a method for purely probabilistic query expansion that outperforms all methods tested. Finally we explore word sense disambiguation based on ontologies as that is a prerequisite step for ontological query expansion. The ontology used was WordNet. The results of our experiments were based on standard TREC conferences data and showed that an ontological approach can cause improvement over non-ontological methods.