Cooperative access to relational and object-oriented federated databases

Much work has been done in the field of heterogeneous federated database systems (FDBSs), but almost all this work deals with relational systems or, eventually, with the integration of hierarchical and network models and the relational model. The authors present a prototype that allows access to relational (INGRES) and object-oriented (O2) database systems composing a federation. They assume that all databases store equivalent information. Users are allowed to specify queries over one of the component databases and the prototype retrieves equivalent information from the other database using a set of mapping rules. These rules define equivalences between the schemas´ structures of INGRES and O2. The prototype has been implemented in Prolog and C in a network of Sun workstations