Luigi Palopoli Luigi Pontieri Giorgio Terracina Domenico Ursino Intensional and extensional integration and abstraction of heterogeneous databases. 201-237 2000 35 Data Knowl. Eng. 3 db/journals/dke/dke35.html#PalopoliPTU00 http://dx.doi.org/10.1016/S0169-023X(00)00028-8