Att expandera sökfrågor i en elektronisk bibliotekskatalog
En jämförelse av återvinningseffektiviteten för fyra olika sökfrågetyper
This Masters thesis deals with query expansion in an online library catalogue. The aim of the study was to compare the retrieval effectiveness of four different query types when applied to the online library catalogue of the University College of Borås. The query types were: an initial query, the initial query with right hand truncation, the initial query expanded with synonyms and finally the initial query expanded with synonyms and right hand truncation. 24 topics were formulated, and four queries for each topic were constructed. The records retrieved by the searches were judged with regard to topicality, and were judged to be non-relevant, partially relevant or relevant. Formulation of topics and relevance judgements were carried out by persons with a certain knowledge of subjects represented in the library catalogue. These persons also constituted the source of search terms. The retrieval effectiveness of the query types was evaluated regarding to relative recall and precision. It was found that expansion of the initial queries improved the retrieval effectiveness, both regarding to relative recall and precision. The most expanded query type showed the best result by far with respect to relative recall. With regard to precision, the best performing query type was the initial query with right hand truncation. Finally, false drops retrieved by the searches were analysed and classified. This analysis showed that false drops caused by the content of records constituted more than half 55 % of the false drops. The remaining 45 % consisted of false drops caused by the search terms.