Open Access

Inspired by the current Semantic Web developments that foster the publication of domain ontologies and semantically annotated data, this thesis investigates how such ontological structures can be used for query expansion purposes. The thesis analyzes how a research context ontology can be used for query expansion purposes in a retrieval system for the domain of educational research, the German Education Index. To assess the potential of ontology based query expansion in this application context, a retrieval prototype with different levels of ontology based query expansion support is implemented. Large-scale automatic retrieval experiments systematically analyze the expansion effects of several types of semantic relations, showing that an expansion term's semantic relation to an original query term affects the expansion term’s effectiveness. Based on these findings, ontology relations for the generation of automatic and interactive query expansion terms are identified and implemented in an interactive retrieval prototype. Its ontology based query expansion mechanisms are evaluated in interactive retrieval experiments that compare the automatic and interactive expansion mechanisms' effects at the level of search sessions, both in terms of retrieval effectiveness and in terms of their impact on the users’ query (re-)formulation behavior.