Tractable Cover Compilations

Yacine Boufkhad, Éric Grégoire, Pierre Marquis, Bertrand Mazure, Lakhdar Sais

Abstract: Tractable covers are introduced as a new approach to equivalence-preserving compilation of propositional knowledge bases. First, a general framework is presented. Then, two specific cases are considered. In the first one, partial interpretations are used to shape the knowledge base into tractable formulas from several possible classes. In the second case, they are used to derive renamable Horn formulas. This last case is proved less space-consuming than prime implicants cover compilations for every knowledge base. Finally, experimental results show that the new approaches can prove efficient w.r.t. direct query answering and offer significant time and space savings w.r.t. prime implicants covers.