P2P deductive databases: A system prototype

This paper proposes a system prototype for query answering in a Peer-to-Peer (P2P) network. As usual, a query can be posed to any peer in the system and the answer is provided by using locally stored data and all the information that can be consistently imported from its neighbors, i.e. the information satisfying integrity constraints collected using the semantic paths of mappings. The work stems from previous works of the same authors in which a declarative semantics for P2P systems is proposed. Under this semantics only facts not making the local databases inconsistent can be imported and the Preferred Weak Models are the consistent scenarios in which peers import maximal sets of facts not violating integrity constraints. In the general case, as a P2P system may admit many preferred weak models, the computational complexity results to be prohibitive, therefore this paper looks for a more pragmatic solution for assigning semantics to a P2P system. More specifically, it assigns to a P2P system its Well Founded Model, a partial deterministic model that captures the intuition that if an atom is true in a preferred weak model, but it is false in another one, then it is undefined in the well founded model. The paper presents a distributed algorithm for the computation of the well founded model and provides details on the implementation of a system prototype for query answering in P2P network based on the proposed semantics.