Using wrapper agents to answer queries in distributed information systems

Nowadays, one of the objectives of information integration is to provide a global view of the information contained in a set of information sources. This is an important objective as global views enable us to design applications that use information contained in a set of autonomous and heterogeneous information sources. The global view is represented using a global schema, which is usually different from the schemata of the information sources. Users interested in exploiting the global information must be aware of the global schema. One of the drawbacks of this approach is that users working with local applications, who are often interested in exploiting global information, cannot access global information using their own local applications, as the latter are based on local scemata and are hardly adaptable to the global schema. What we envisage is the possibility for local applications of exploiting information contained in other information sources through their local schema. As an important effect, users can utilize global information via their usual local applications. The architecture we adopt is based on a multi-agent structure. In this structure there is no central agent, which plays the role of a mediator to integrate all the information sources. The key role in the process of information integration is played by the wrapper agents. Wrapper agents (or simply wrappers) are provided both for each information source and, if any, for each global view