Abstract
After a relation schemeR is decomposed into the set of schemesρ={R 1,...,Rn}, we may pose queries as ifR existed in the database, taking a join ofR i’s, when it is necessary to implement the query. Suppose a query involves a set of attributesS⊆R, we want to find the smallest subset of ρ whose union includesS. We prove that the problem is NP-complete and present a polynomial-bounded approximation algorithm. A subset of ρ whose union includesS and has a decomposition into 3NF with a lossless join and preservation of dependencies is given in the paper.
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References
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Ellis Horowitz and Sartaj Sahani, Fundamentals of Computer Algorithm, Computer Science Press, Potomac, Md., 1978.
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Liu, W. An efficient algorithm for processing multi-relation queries in relational databases. J. of Comput. Sci. & Technol. 5, 236–240 (1990). https://doi.org/10.1007/BF02945311
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DOI: https://doi.org/10.1007/BF02945311