Effekten av avståndsoperatorer samt expansion med synonymer med avseende på återvinningseffektiviteten
This thesis examines the effects of proximity operators and query expansion with synonyms on retrieval performance. The queries were expanded with synonyms and structured with proximity operators where the permitted distance between terms varied from 1 to 3. The expansion terms were selected from the online lexical reference system WordNet. Initial query terms were selected from 28 topics that contained compound words and were chosen on the basis of their expandibility. The English morphological analyser ENGTWOL was used for normalization of query terms. Queries were executed in the Interactive Query Performance Analyser, QPA, containing the InQuery system. The test collection used was TREC-UTA containing documents, topics and a set of relevant documents per given topic. The measures used in the study were average precision, precision at 10 retrieved documents and recall at 200 retrieved documents. The results of the study show that query expansion with synonyms did not improve retrieval performance and neither did query structuring with proximity operators. This result was in a way surprising since earlier studies have obtained improvements when queries were expanded and structured. Further investigation on phrases using proximity operators was also suggested.