RDB has been dominant in the industry for the last decade. OODB is recognized as a post-relational technology that can improve productivity. Hierarchical Database and Network Database were popular in the 1970s, and have been developed into legacy database systems. The DBMS of various data models have proliferated into many companies, and become their important assets. There is a need to integrate these database system into a data warehouse in the company. We investigate a solution to the problem by offering an architecture of a universal database for the connectivity of various DBMSs using different data models. A frame model is chosen to represent the conceptual and logical schema of the universal database, which structures an application domain into classes organized via generalization, aggregation and user-defined relationships, and its data in relational tables. The schemas of the existing database systems are translated into frame model conceptual schemas which are integrated into a global frame model in a knowledge representation that includes classes for object structure descriptions and constraints for supporting user-defined relationships. The universal database is implemented by a relational DBMS as a kernel. In addition to relational tables, the universal database consists of program area to emulate database navigation in nonrelational DBMS, method classes to implement program calls to emulate methods of OODBMS, and constraint classes to preserve semantic and resolve naming conflicts in schema translation and integration. To ensure each database program access the universal database, a database gateway for each source DBMS is developed to translate their DML into SQL, which is chosen to be its kernel database language, for its user-friendliness, standardization and popularity in the industry.
