Expanding end-users' query statements for free text searching with a search-aid thesaurus

摘要

Authors and searchers usually express the same things in many different ways, which causes problems in free text searching of text databases. Thus, a switching tool connecting the different names of one concept is needed. This study tests the effectiveness of a thesaurus as a search-aid in free text searching of a full text database. A set of queries was searched against a large full text database of newspaper articles. The search-aid thesaurus constructed for the test contains the usual relationships of a thesaurus, namely equivalence, hierarchical, and associative relationships. Each query was searched in five distinct modes: basic search, synonym search, narrower term search, related term search, and union of all previous searches. The basic searches contained only terms included in the original query statements. In the synonym searches, the terms of the basic search were extended by disjunction of the synonyms given by the search-aid thesaurus without modifying the overall logic of the basic search. Likewise, the basic search was extended in turn with the narrower terms and with the related terms given by the search-aid thesaurus. The last search mode included the basic terms and all the terms used in the previous searches. The searches were analyzed in terms of relative recall and precision; relative recall was estimated by setting the recall of the union search to 100%. On the average the value of relative recall was 47.2% in the basic search, compared with 100% in the union search; the average value of precision decreased only from 62.5% in the basic search to 51.2% in the union search.