Optimizing entity join queries by extended semijoins in a wide area multidatabase environment

We consider processing entity join queries in a wide area multidatabase environment where the query processing cost is dominated by the cost of data transmission. An entity join operation ”integrates” tuples representing the same entities from different relations in which inconsistent data may exist. The semijoin technique has been successfully used in a distributed database system to reduce the cost of data transmission. However, it cannot be directly applied to process the entity join query. An extension of the traditional semijoin, named extended semijoin is proposed to reduce the cost of data transmission for entity join query processing in a wide area multidatabase environment