Abstract
In this paper, we study the problem of data integration in P2P systems. Differently from the traditional setting, data integration in these systems is not based on the existence of a global view. Instead, each peer exports data in terms of its own schema, and information integration is achieved by establishing mappings among the various peer schemas. We present a framework that captures this general architecture, and then we discuss the problem of characterizing the semantics of such framework. We show that the usual approach of resorting to a first-order logic intepretation of P2P mappings, leads both to a poor modeling of the whole system, and to undecidability of query answering, even for mappings of a restricted form. This motivates the need of a new semantics for P2P system. We then present a novel proposal, based on epistemic logic, and show that not only it adequately models the interactions among peers, but it also supports decidable query answering. In particular, for the restricted form of mapping mentioned above, query answering is polynomial with respect to the size of data stored in the peers.