Modeling Cooperation in P2P Data Management Systems

This paper investigates the data exchange problem among distributed independent sources. It is based on previous works in [9,10] in which a (declarative) semantics for P2P systems. In this semantics only facts not making the local databases inconsistent are imported

Weak Models

, and the

Preferred Weak Models

are those in which peers import maximal sets of facts not violating integrity constraints. The framework proposed in [9,10] does not provide any mechanism to set priorities among mapping rules. Anyhow, while collecting data it is quite natural for a source peer to associate different degrees of reliability to the portion of data provided by its neighbor peers. Starting from this observation, this paper enhances previous semantics by using priority levels among mapping rules in order to select the weak models containing a maximum number of mapping atoms according to their importance. We will call these weak models,

Trusted Weak Models

and we will show they can be computed as stable models of a logic program with weak constraints.