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.