An object of the present invention is to avoid contention for resources in a parallel/decentralized database system so as to improve the performance of the system. A query posing method is implemented in a database system comprising a plurality of database servers each of which includes a database from which the same content can be retrieved and searches the database in response to a query request a front-end server that poses a query according to a predetermined rule and a management server that manages rules to be used by the front-end server. The management server acquires a processed query log relevant to a database server, and produces a rule according to the compatibility value of a query calculated using the acquired processed query log. Moreover, the front-end server poses the query according to the rule produced by the management server.