Algorithms to Process Distributed Queries in Fast Local Networks

We propose a scheme to make use of semantic information to process distributed queries locally without data transfer with respect to the join clauses of the query. Since not all queries can be processed without data transfer, we give an algorithm to recognize the "locally processable queries." For nonlocally processable queries, a simple "fragment and replicate" algorithm is used. The algorithm chooses a relation to remain fragmented at the sites where they are situated while replicating the other relations at those sites. Our algorithm determines the chosen relation and the chosen copy of every fragment of the chosen relation such that the minimum response time is obtained. The algorithm runs in linear time. If the fragments of the relation are allowed to be processed in other sites, then the problem is NP hard. Two heuristics are given for that situation. They are compared to the optimal situation. Experimental results show that the strategies produced by the heuristics have small errors relative to the optimal strategy.