INFORMATION PROCESSING APPARATUS, DOCUMENT RETRIEVAL SYSTEM, DOCUMENT RETRIEVAL METHOD, AND PROGRAM

An information processing apparatus includes a database management unit that generates an index including access authority for a document and manages the index together with the document, a user information acquisition unit that acquires, as user information, the access authority for a user identification value, a document search unit that acquires the user information and a search request including a search expression, generates a combined search expression by combining an inclusion relationship expression with the search expression, the inclusion relationship expression including an operator that designates an inclusion relationship for access authority of an originator, and acquires a search result at a shared level enabling sharing under a plurality of user identification values in a domain including the plurality of user identification values, and a cache management unit 218 that registers the search result at the shared level as a cache item identified as the one at the shared level.