Base and derivative structural concepts of ERM data model and isomorphic relation between them

Model «Entity-Relationship-Mapping» is obliged to its initial name to two base concepts of model - «object» and «mapping». Later for convenience of DB designing it got traditional concepts of Chen's ER-model as derivatives from its base concepts, and the ERM-model has been formed. Each of structural concepts groups - base and derivative, plays its role during designing -the first provides expressive power and mathematical validity of the model, the second facilitates understanding of model by person. For use of both structural concepts groups by complementary manner rules of ERM-schemas transformation from derivative concepts language to base concepts language and vice versa are offered. They allow to carry out the one-to-one transformations of schemas necessary for completion of the schemas, check on consistency and transformations to the DBMS models serving as target models of process of DB designing. Thus, it is shown, that the isomorphic relation exists between these two systems of concepts. Its presence allows building a technique of schemas designing, combining advantages of both concepts systems. On the steps of such technique elements of one system can unambiguously be translated in elements of other system and vice versa.

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