De.clare-a deductive database system with heterogeneous access to relational database systems

The deductive database system De.clare offers a tight coupling to heterogeneous relational database systems. Tight coupling means that there is no semantical gap between the evaluation and optimization strategies of the deductive database system and the corresponding strategies used by relational database systems. This could be achieved by using the bottom-up approach for computing the answer of a query to a deductive database. In particular, this bottom-up approach means that a query to a deductive database system is translated into a relational algebra expression. Then those subqueries are identified that can be evaluated on a relational database system. After the answers to these subqueries have been computed, the results are combined on a relational database system which offers an extended relational algebra and finally the answer of the original query is computed