Rewriting queries using views

In this paper, we consider the problem of. answering queries using material ized views in the presence of negative goals. The solution is carried out b y "inverting" views and deriving both positive and negative knowledge. In o rder to derive negative knowledge, we invert conjunctive views with negatio n into a set of (extended) views which may also have, in addition to negati on-as-failure, a different form of negation called classical (or strong) ne gation. We also consider the case of disjunctive views and present. a techn ique which permits us to infer both positive and negative knowledge. Furthe rmore, we extend previous techniques for inferring knowledge from views bas ed on relations with functional dependencies. Finally, we present a prototy pe of a system developed at the University of Calabria.