1. A database management system for operating a database by performing a data processing procedure with respect to the database which is defined by a data type, said database management system comprising: a file for storing a correspondence between a user defined extended data type and a standard data type; a library for storing a load module corresponding to a user defined extended data processing procedure; a catalog for storing a correspondence between a user defined data type/data processing procedure and a definition of the data type/data processing procedure; and, a controller for analyzing a command request inputted by a user and for controlling access to said database by using said correspondence in said file and said load module in said library on the basis of said correspondence in said catalog.