A pattern based approach to answering factoid, list and definition questions

Finding textual answers to open-domain questions in large text collections is a difficult problem. In this paper we concentrate on three types of questions: factoid, list, and definition questions and present two systems that make use of regular expression patterns and other devices in order to locate possible answers. While the factoid and list system acquires patterns in an off-line phase using the Web, the definition system uses a library of patterns identified by corpus analysis to acquire knowledge in an on-line stage for each new question. Results are reported over the question sets from the question answering track of the 2002 and 2003 Text REtrieval Conference (TREC).

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