To obtain information having a relation, it is required for an application program to execute retrieval processing in which the program first acquires key information supervising relations between tables to sequentially trace the relations to finally obtain the target information. Since it is required for the program to execute as many access operations as there are hierarchic level of relations, the access efficiency is lowered. By establishing a correspondence between first relating information representing relations between a first table and a second table and second relating information, path information representing hierarchic structure of data between a plurality of tables is stored in a storage. Various processings are executed by use of the path information.