{38 () Query Reformulation for Dynamic Information Integration

The standard approach to integrating heterogeneous information sources is to build a global schema that relates all of the information in the di erent sources, and to pose queries directly against it. The problem is that schema integration is usually di cult, and as soon as any of the information sources change or a new source is added, the process may have to be repeated. The SIMS system uses an alternative approach. A domain model of the application domain is created, establishing a xed vocabulary for describing data sets in the domain. Using this language, each available information source is described. Queries to SIMS against the collection of available information sources are posed using terms from the domain model, and reformulation operators are employed to dynamically select an appropriate set of information sources and to determine how to integrate the available information to satisfy a query. This approach results in a system that is more exible than existing ones, more easily scalable, and able to respond dynamically to newly available or unexpectedly missing information sources. This paper describes the query reformulation process in SIMS and the operators used in it. We provide precise de nitions of the reformulation operators and explain the rationale behind choosing the speci c ones SIMS uses. We have demonstrated the feasibility and e ectiveness of this approach by applying SIMS in the domains of transportation planning and medical trauma care.