A6Ans - University of Waterloo School of Computer Science...

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University of Waterloo School of Computer Science CS348 Spring 2009 Assignment 6 Due: July 14, 2009 1. 30%(a) Let F = {AB C, A D, BD C, C A} be the set of fd’s on R(ABCD). Find all candidate keys of R. Explain your answer. To find all keys, enumerate all possible subsets and test for minimality and that the subset determines all attributes in R. With the help of the closure algorithm for a set of attributes, the students need to show that BD,BC,AB are the keys and are the only keys. 70%(b) Let S={AB,BCD,AD} be a decomposition of R. For each relation scheme in S, find all projected fd’s. Is S in 3NF? Is S in BCNF? Is S a lossless decomposition? Is S dependency preserving? Explain your answers. 20% To find all non-trivial projected fd’s, consider all possible fd’s defined on the corresponding relation scheme. That is, the students need to show that they consider all possible nontrivial fd’s X A and see if they are in the closure of F. AB: no non-trivial fd.
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