Dictionary and index creating system and document retrieval system

Abstract

A high-speed document retrieval system creates a regular expression dictionary and a word index on the basis of a retrieval document and a word dictionary to conduct retrieval to a document through the regular expression dictionary and the word index at a high speed. A regular expression dictionary expressing a set of character strings having the same length is created from a word dictionary. In terms of a character string included in a retrieval document and matching with a regular expression in the regular expression dictionary, an index element is recorded in a word index when there is no different index element which allows an observing index element to be deducible, which eventually produces a word index capable of achieving a high-speed full-text retrieval without the noticeable increase in the index capacity. The document retrieval system performs the retrieval of the retrieval document through the use of the word dictionary, the regular expression dictionary and the word index, so that a high-speed full-text retrieval is possible without the impairment of retrieval efficiency even if the retrieval character string is covered with words having a small number of characters and making less overlap.