Multidatabase query optimization

A multidatabase system (MDBS) allows the users to simultaneously access heterogeneous, and autonomous databases using an integrated schema and a single global query language. The query optimization problem in MDBSs is quite different from the query optimization problem in distributed homogeneous databases due to schema heterogeneity and autonomy of local database systems. In this work, we consider the optimization of query distribution in case of data replication and the optimization of intersite joins, that is, the join of the results returned by the local sites in response to the global subqueries. The algorithms presented for the optimization of intersite joins try to maximize the parallelism in execution and take the federated nature of the problem into account. It has also been shown through a comparative performance study that the proposed intersite join optimization algorithms are efficient. The approach presented can easily be generalized to any operation required for intersite query processing. The query optimization scheme presented in this paper is being implemented within the scope of a multidatabase system which is based on OMG's object management architecture.