Query Optimization Using Local Completeness

We consider the problem of query plan optimization in information brokers. Information brokers are programs that facilitate access to collections of information sources by hiding source-speciic peculiarities and presenting uniform query interfaces. It is unrealistic to assume that data stored by information sources is complete. Therefore, current implementations of information brokers query all possibly relevant information sources in order not to miss any answers. This approach is very costly. We show how a weaker form of completeness, local completeness, can be used to minimize the number of accesses to information sources.