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W.W. Chu, Department of Computer Science, School of Engineering and Applied Science, University of California
In the above paper1, Theorem 1 is not true in general. The purpose of Theorem 1 was to reduce the number of feasible query trees by determining the optimal positions of unary operations in a given query tree. In fact, Theorem I is true only if the processing cost of a unary operation is independent of the volume of input data.
Citation:
W.W. Chu, P. Hurley, "Correction to "Optimal Query Processing for Distributed Database Systems"," IEEE Transactions on Computers, vol. 32, no. 9, pp. 878, Sept. 1983, doi:10.1109/TC.1983.1676340
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