ABSTRACT

In this paper, we study the problem of consistent query answering in peer data sharing systems. In a peer data sharing system, databases in peers are designed and administered autonomously and acquaintances between peers are established thorough data sharing constraints. Since data are managed in peer databases autonomously, peers' data may be inconsistent with respect to the data sharing constraints. Inconsistencies of data may also result due to the change of constraints (e.g. adding, modifying, and deleting constraints between peers). In order to solve inconsistencies between peers, one possible solution could be modify data physically in inconsistent peers by propagating updates. However, it is not always feasible to change data physically in peers since peers are autonomous and a peer may not have permission to modify other peers' data. Considering the possible inconsistent situations, this paper presents a semantics of obtaining consistent answers in a peer data sharing system such that the answers are consistent wrt to data sharing constraints. Consistent answers are obtained at query time by avoiding the inconsistent data. The paper also shows a method to achieve consistent answers of a query.