Patent ID: 6714927
Filing Date: 2004-03-30
Classification: G06F,Y10S

Abstract:
An apparatus for retrieving documents comprising:a document dividing part dividing each document into partial character strings as index keys; an index table maintaining the index keys and document information relating to each index key; a query character string dividing part dividing a query character string into a plurality of index keys; a retrieval condition analyzing part analyzing a retrieval condition including the index keys divided from the query character string and generating a retrieval condition tree where the index keys are synthesized by at least one operator that retrieves an intermediate retrieval result including the document information from said index table; and a retrieval condition evaluating part evaluating each intermediate retrieval result obtained by the retrieval condition tree and determining a final retrieval result, wherein said document dividing part divides the document into index keys of n-character strings having n characters and m-character strings having m characters where n is an integer greater than one and m is an integer less than n, and each of m-character strings includes a last character of the document, wherein, when at least two index keys are divided from the query character string by said query character string dividing part, said retrieval condition analyzing part includes: a first condition tree generating part generating a first condition tree synthesized by at least one AND set operator obtaining an AND set of a plurality of the intermediate retrieval results based on said at least two index keys; and a second condition tree generating part selecting a minimum number of index keys, which cover a full length of the query character string, from said at least two index keys and generating a second condition tree synthesized by at least one distance operator indicating a distance between appearance positions of said at least two index keys, wherein: said retrieval condition analyzing part includes a document determining part obtaining candidate documents by executing the first condition tree and determining documents from the candidate documents by calculating a second condition tree; and said first condition tree generating part generates the first condition tree by index keys used in the second condition tree and other index keys positioned in the query character string before or after the index keys used in the second condition tree and indicating a least number of the documents including the other index keys.