【摘 要】
：
After a relation scheme R is decomposed into the set of schemes ρ={R_1,...,R_n},we may posequeries as if R existed in the database,taking a join of R_i’s,whe
【机 构】
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Yunnan University,
【出 处】
：
Journal of Computer Science and Technology
论文部分内容阅读
After a relation scheme R is decomposed into the set of schemes ρ={R_1,...,R_n},we may posequeries as if R existed in the database,taking a join of R_i’s,when it is necessary to implement thequery.Suppose a query involves a set of attributes S(?)R,we want to find the smallest subset of ρwhose union includes S.We prove that the problem is NP-complete and present a polynomial-boundedapproximation algorithm.A subset of ρ whose union includes S and has a decomposition into 3NF witha lossless join and preservation of dependencies is given in the paper.
We may posequeries as if R existed in the database, taking a join of R_i’s, when it is necessary to implement thequery.Suppose a query involves a set of attributes S (?) R, we want to find the smallest subset of ρwhose union includes S.We prove that the problem is NP-complete and present a polynomial-boundedapproximation algorithm. A subset of ρ whose union includes S and has a decomposition into 3NF witha lossless join and preservation of dependencies is given in the paper.
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