Titlebook: Database Theory - ICDT ‘95; 5th International Co Georg Gottlob,Moshe Y. Vardi Conference proceedings 1995 Springer-Verlag Berlin Heidelberg

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委屈

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BATE

Distributed query optimization in loosely coupled multidatabase systems,ion process is organized as a sequence of steps, in which at each step all . work in parallel to evaluate the cost of execution plans for partial queries of increasing size, and send their cost estimates to the other . that need them for the next step. The computation is totally distributed, and org

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On the complexity of generating optimal left-deep processing trees with cross products,marizing the intermediate result sizes has the ASI property. It further motivates us to restrict the subsequent investigations to this cost function called .. for which we show that the problem remains NP-complete in the general case..Then, we concentrate on the main topic of the paper: the complexi

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Querying disjunctive databases through nonmonotonic logics, autoepistemic logic and some of their fragments express the same class of Boolean queries, which turns out to be a strict subclass of the ..-recognizable Boolean queries. Then we prove that under the assumption that the database consists of clauses whose length is bound by some constant, default lo

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