On the implementation of a conceptual schema model within a three-level DBMS architecture

The ANSI/X3/SPARC study group on database management systems 2 as well as some independent researchers 17 , 10 have proposed a three-level "coexistence" architecture to database management systems. Under this approach (see Figure 1 ) a number of different users can be supported by means of different External Schemas, possibly with different data models and languages. It involves construction of a conceptual schema which completely represents the structure and semantics of a particular database. The underlying internal schema must provide a storage representation for the conceptual schema. Although the composition and scope of the conceptual schema is still a matter of controversy, 1 several data models, semantic models (e.g., References 7 , 8 , 9 , 13 , 16 , 20 , 21 ) etc. could be considered as candidates for defining conceptual schema. Given a particular model for the conceptual schema, a number of problems arise in its implementation into a three-level DBMS, particularly regarding the design of an internal schema specification language to specify the mapping of the model into storage.