Query optimization in multidatabase systems: solutions and open issues

Query optimization in multidatabase systems differs from that of distributed homogeneous database systems due to the lack of information about cost formulae of component local database systems as well as due to less control over local query execution. The paper provides an overview of query processing in multidatabase systems. It includes the architecture of a multidatabase system, query execution model and multidatabase query optimization. Some results are surveyed and some open issues are discussed