Dealing with incompleteness and inconsistency in P2P deductive databases

This paper proposes a logic framework for modeling the interaction among incomplete and inconsistent deductive databases in a P2P environment. Each peer joining a P2P system provides or imports data from its neighbors by using a set of mapping rules, i.e. a set of semantic correspondences to a set of peers belonging to the same environment. By using mapping rules, as soon as it enters the system, a peer can participate and access all data available in its neighborhood, and through its neighborhood it becomes accessible to all the other peers in the system. Two different types of mapping rules are defined: a first type allowing to import maximal sets of atoms and a second type allowing to import minimal sets of atoms from source peers to target peers. In the proposed setting, each peer can be thought of as a resource used either to enrich (integrate) the knowledge or to fix (repair) the knowledge. The declarative semantics of a P2P system is defined in terms of preferred weak models. An equivalent and alternative characterization of preferred weak model semantics, in terms of prioritized logic programs, is also introduced. The paper also presents preliminary results about complexity of P2P logic queries.