PURPOSE: To easily change data structure without changing any schemer by preparing the schemer of a document as the attribute of a document class and changing the data structure by addition/deletion of the attribute.

CONSTITUTION: Concerning a data base managing system in which the data structure to be preserved in an object orientated data base is defined while using the schemer, the document class does not directly have the attribute but has a link with an attribute object and the schemer is designed as the attribute class of the document class. Concerning the attribute class, an attribute name and attribute contents are described as the attribute and the change of the attribute name or the like is described as an operating function. Then, the change of data structure is performed by adding or deleting the attribute of the document. Thus, the data structure can be changed without changing any schemer. Besides, the attribute is added or deleted from an application program and further, the recompile of the schemer and application program is unnecessitated.