Issues in Supporting Interoperable Query Processing with Multiple Heterogeneous Information Servers 1

This project has three goals. First, we support interoperable query processing among multiple heterogeneous sources. Heterogeneity arises due to the existence of diierent data models, schema and query languages. For an initial query posed w.r.t. a schema and query language, we produce mediated (transformed) queries w.r.t. other schema/query languages. The second goal is to modify traditional query optimization techniques so that they may be applied in a heterogeneous environment, to produce optimized mediated queries. Finally, we develop a sound theory for information mediation. We identify criteria for the correct speciication of the mediation knowledge base, criteria to determine when a mediated query is correct, and when a mediated answer is consistent.