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Abstract |
A meta-model for database models called an abstract relational model which is obtained by a categorical abstraction of a relational model is proposed. This meta-model represents various database model...s, e.g. relational, network, hierarchical models as special cases. It is proved that a natural join is the right adjoint of a decomposition in the relational model. On the other hand, in our abstract relational model a natural join is defined as the right adjoint of a decomposition. A sufficient condition is shown for a database model to have natural joins.show more
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