Duetal. have proposed an algorithm to translate a left deep join tree into a balanced bushy join tree for a multidatabase query. In this paper, we refine that algorithm by extending the basic transformation step used in it so that a more balanced join tree can be obtained. In addition, by taking the transmission costs as well as the workloads of local database systems into account, we develop an efficient algorithm for query plan generation such that both the tree balance and the node allocation can be achieved.
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