Patent ID: 7689545

Claim:
A document retrieval method for searching a document database for documents matching a specified query condition using a system management server, a plurality of search servers and a storage device, comprising the following steps performed by: (1) the storage device, arranged to: (1)-1: store information for identifying each of the plurality of search servers; (1)-2: store a character string included in the documents with an association to: a document identifier of a document including the character string; and a page identifier of a page on which the character string is indexed; and (1)-3: store a document range with an association to the character string and the page identifier on which the character string is indexed; (2) the system management server, arranged to: (2)-1: receive the specified query condition from the storage device, and determine a range of documents to be searched by each of the search servers according to: the specified query condition, and the document identifier and the page identifier stored in the storage device, (2)-2: send information on: the range of documents determined to be searched to the storage device at which the range of documents to be searched is recorded, and the specified query condition to each of the search servers at which the specified query condition is recorded; (3) each of the plurality of search servers, arranged to: (3)-1: acquire a document identifier, and acquire a page identifier based on the document identifier, for each of the plurality of search servers, and (3)-2: perform a search operation of the document database at each of the search servers based on the specified query condition and the acquired page identifier; and (4) the system management server, further arranged to: (4)-1: output a total search operation result derived from the search operations performed for all of the plurality of search servers; wherein the system management server is further arranged to: compare processing costs for indexes when the indexes for two or more character strings are referred to execute the searching operation; and determine the range of documents set for the character string having the larger processing cost as the range of documents for all the character strings as a result of said comparison.