Rewriting queries using views

In this paper, we consider the problem of. answering queries using materialized views in the presence of negative goals. The solution is carried out by "inverting" views and deriving both positive and negative knowledge. In order to derive negative knowledge, we invert conjunctive views with negation into a set of (extended) views which may also have, in addition to negation-as-failure, a different form of negation called classical (or strong) negation. We also consider the case of disjunctive views and present. a technique which permits us to infer both positive and negative knowledge. Furthermore, we extend previous techniques for inferring knowledge from views based on relations with functional dependencies. Finally, we present a prototype of a system developed at the University of Calabria.