Using wrapper agents to answer queries in distributed information systems

Most of the reference architectures for information integration are based on the notion of mediator, which provides an homogeneous and global view of a set of heterogeneous information sources. Mediators enable global applications to access heterogeneous information contained in different sources in a transparent way. In these architectures, however, the single information sources do not have any added value from being integrated. In this paper we investigate a more `cooperative` approach, in which each information source directly interacts with the others as it were a mediator, so that it can obtain new information by directly querying the other information sources. The architecture proposed in this paper is based on a multi-agent structure, and its main components are wrapper agents. We provide a formal model for the architecture, and we specify a set of basic tasks that must be supported by all wrapper agents in order to support query answering. A first (unoptimized) implementation of these tasks, which is correct and complete w.r.t. the formal model, is also presente