Information Retrieval (IR) deals with information search in purely structured data like e.g. full texts or multimedia databases. Popular applications are web search engines, digital libraries and multimedia archives (e.g. for images).Due to the vagueness of the information need and the uncertain representation of the content of the stored objects, standard database techniques are not appropriate. Instead, the concepts have to be extended to deal with vagueness and uncertainty. As the major focus is on content-oriented search, special techniques for representing the content of text and multimedia objects are required.