Abstract: A database management system includes an object conversion unit converting each of a plurality of natural objects and each of a plurality of object IDs of consecutive data according to a predetermined rule in a unique relationship and a bidirectional manner; and a database storing tables of a hierarchical structure including the object IDs converted by said object conversion unit as a permanent object holding data during a period. The tables of the hierarchical structure have a data structure formed by connecting a lower table and another lower table through at least one upper table on a chain and in a bidirectional manner.