Methods of Extracting Year References for Chronological-table-generating Text Searching

Abstract

A method of extracting year references for a textual information retrieval method called the thematic chronological-table search method is explained in this paper. This search method generates an index by extracting and collecting year references from a text collection. The resulting index and a full-text index are used for searching sentences that contain year references and search words. The results are displayed in the form of a chronological table with hyperlinks to the original text. Seven forms of year or century references are extracted and normalized using string matching patterns. The extraction error rate is reduced by using both local and non-local contexts. If the lower two digits of a Gregorian year, which matches a form, occurs, it is normalized by supplementing the upper digits using the non-local context. This method has been applied to a Japanese encyclopedia. An evaluation shows the precision of extraction to be higher than 99 % in most cases