Executing Joins Dynamically in Distributed Database System Query Optimizer

In order to join two sub queries involving data from multiple sites data has to be transmitted from one site to other.While transmitting the data within a network, the factors involved in distributed databases is communication cost and amount of data transmitted.To minimize these factors, join operation is used.There are two cases considered in which query processing using join and query processing using semi join are described.The amount of data transfer in case of join is more than in case of semi join.Hence sub operations are executed dynamically to improve the communication cost .