Abstract: Recently, there is a growing need for query optimization that can effectively deal with federated database systems. Modern optimizers use a cost model to choose the best query execution plan (QEP) which heavily dependent on statistics maintained in the system catalog. Keeping such statistics up to date in the federation is troublesome due to local autonomy.This paper discuss query processing for a federated data base system. The main objective of the paper is to give general framework for query optimization in federated database system and enhancing the global query optimization.
Keywords: Federated Query Optimization, Query Execution Plan (QEP), Query Processing, Database System.