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Journal of Inforamtion Science and Engineering, Vol. 16 No. 4, pp. 463-497 (July 2000)

A Systematic Method for Query Evaluation in Distributed
Heterogeneous Databases

Yangjun Chen
IPSI Institute, GMD GmbH
64293 Darmstadt, Germany

In this article, we consider the query evaluation problem in relational multidatabases and develop a method for generating optimal plans for queries submitted to such a system. Three aspects will be discussed: query transformation, join tree balance and node allocation. For query translation, the concept of relation structure terms (RST) is introduced. Based on RSTs, we can transform a query into another form automatically by constructing derivation rules for them. Further, we extend the approach for balancing a join tree proposed by Du et al. so that more balanced join trees can be obtained. Lastly, we present the concept of dynamic time tables for performing node allocation in a dynamic programming manner.

Keywords: heterogeneous databases, join tree balance, relation structure terms, dynamic programming, dynamic time tables

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Received December 28, 1998; revised May 24, 1999; accepted July 19, 1999.
Communicated by Wei-Pang Yang