Full-text search apparatus utilizing two-stage index file to achieve

Abstract

A new type of text search apparatus, capable of finding all occurrence positions of a search string that is an arbitrary character string, within a text which is written as a continous sequence of characters, utilizes for text position reference purposes in an index file, words which each occur (at least once within the text) as the maximum length word, referred to as an extension word, among a set of arbitrarily predefined dictionary words extending from a specific character position. Each such occurrence of a word as an extension word defines one of a set of text position elements, with that set covering all of the character positions of the text. The index file also includes a table which relates each of the extension words to the respective positions at which each of the partial character strings of the word occur within the word. Each occurrence of an arbitrary search string within the text can thereby be expressed as either a partial character string within a single text position element, or as a sequence of partial character strings within a set of sequentially occurring text position elements, so that all such occurrences can be found by utilizing the index file.