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Unformatted text preview: 190 Chapter 19 3. Consider the set of FD: AB CD and B C . AB is obviously a key for this relation since AB CD implies AB ABCD . It is a primary key since there are no smaller subsets of keys that hold over R(A,B,C,D) . The FD: B C violates 2NF since: C B is false; that is, it is not a trivial FD B is not a superkey C is not part of some key for R B is a proper subset of the key AB (transitive dependency) 4. Consider the set of FD: AB CD and C D . AB is obviously a key for this relation since AB CD implies AB ABCD . It is a primary key since there are no smaller subsets of keys that hold over R(A,B,C,D) . The FD: C D violates 3NF but not 2NF since: D C is false; that is, it is not a trivial FD C is not a superkey D is not part of some key for R 5. The only way R could be in BCNF is if B includes a key, i.e. B is a key for R. 6. It means that the relationship is one to one. That is, each A entity corresponds to at most one B entity and viceversa. (In addition, we have the dependencyentity and viceversa....
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This note was uploaded on 01/17/2012 for the course EGN 4302 taught by Professor Dr.vishak during the Fall '12 term at University of Central Florida.
 Fall '12
 Dr.Vishak

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