Information searching apparatus for searching text to retrieve character

Abstract

A plurality of characters arranged in a text are numbered in order of occurrence for each character type, and an occurrence number table in which one or more occurrence numbers are listed for each character type is prepared in an occurrence number preparing unit. Also, a set of two character types is defined as a character pattern, and a set of two occurrence numbers of two adjacent characters of which types correspond to one character pattern is defined as an occurrence number pattern. One or more occurrence number patterns respectively corresponding to one character pattern are arranged for each character pattern, and a list of occurrence number patterns is prepared as an index file in an index file preparing unit. Thereafter, a series of specified character patterns indicated by a key word is prepared, and a series of particular occurrence number patterns corresponding to the series of specified character patterns is selected on condition that a series of particular characters indicated by the series of particular occurrence number patterns agrees with the particular character stream. Therefore, because the characters of the text is converted to the occurrence number patterns and all occurrence number patterns are not searched, a searching operation can be performed at a high speed.