A3sol

# A3sol - Question 1[30 Marks a[5 Marks Explain why a...

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Question 1 [30 Marks] a) [5 Marks] Explain why a relation with only two attributes is always in BCNF, regardless of functional dependencies. A : either a-> or b->a, one of the attribute must be the superkey, because it can determine every attribute in the table. If the only FD is a,b -> a or a,b -> b, then this FD is trivial. This relation is still in BCNF. b) [5 Marks] Explain why a relation with n attributes and only trivial functional dependencies is always in BCNF. A : All FDs are trivial. By definition it is in BCNF. c) [10 Marks] Consider the following database Relation R [a,b,c,d,e] with no duplicate records and with the following FDs: a,b -> c a -> d b -> e b -> d R is decomposed into the following tables: S [a, b, c] T [ b, e ] W [ b, d ] Is that a lossless decomposition of R? Why? [3 Marks] Is that a dependency preserving decomposition of R? Why? [3 Marks] Is that a BCNF decomposition? Why? [4 Marks] A : It is lossless decomposition. S intersect T = {b} -> T , S intersect W = {b} -> W, etc.

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## This note was uploaded on 05/28/2011 for the course CS 338 taught by Professor I.i during the Winter '09 term at Waterloo.

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A3sol - Question 1[30 Marks a[5 Marks Explain why a...

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