Querying Independent Databases

We propose a simple method of providing integrated access to a collection of preexisting, heterogeneous databases connected over a computer network. The user is presented with a collection of unmerged local schemas that have been translated into the relational model. He then expresses his query as selections and projections on some abstract concept. Although the abstract concept may not be explicitly represented in any of the underlying local schemas, the user must be able to relate it to relations in the local schemas in terms of "is-a" relationships. The system then determines how to present some approximation of the desired information to the user.