An object-oriented data base management system connected to a plurality of data bases includes a class definition unit, a static inheritance processing unit included within the class definition unit, a message processing unit, a dynamic inheritance processing unit included within the message processing unit, and an object management unit. The object-oriented data base management system is of the type that defines the inheritance relationship between a plurality of classes and an arbitrary class and the inheritance priority order, the class being a basic unit of programming, and executes the data processing by solving the inheritance relationship between classes in accordance with the priority order. There is prepared, for each class, updatable inheritance solution status information which the static inheritance processing unit causes to be stored in a table. The inheritance solution status information includes status information and time information. The status information is representative of whether or not inheritance between the class and the superclasses can be completely solved, and the time information is representative of a time when the status is established. When a message processing is requested for an object of a class, the dynamic inheritance processing unit searches the method designated by the message while referring to the inheritance solution status information regarding the class and the superclass stored in the table.