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+5 votes

**Answer B)**

A) possible for BCNF. As in BCNF in X-> a transition we take all X as super key and it should be in 3 NF

C) possible

Say a relation AB -> CD

AC -> BD

AD -> BC

All left side are candidate keys and it is in 3NF , So also in BCNF

D) Mutually exclusive foreign keys not a problem for that relational table and also constructing a BCNF

0

Candidate keys are composite

then there is a chance of partial dependency

if partial dependency is there , then relation is not in 2NF

then there is a chance of partial dependency

if partial dependency is there , then relation is not in 2NF

0

Candidate keys are composite then there is a chance of partial dependency; It is okay. If there is no partial dependency then no problem to take composite key as case for BCNF. So I think except D option all are cases for BCNF.

What about the option D, I am not getting meaning of this?

What about the option D, I am not getting meaning of this?

+3

Composite Key is a key which is combination of more than one field or column of a given table. It can be a Candidate key, Primary key. So, a table with combination of its primary key and candidate key can be called as composite key.

Let R(A,B,C,D)

AB->CD and AC->BD. These keys are composite as well as candidate and the relation is in BCNF.

I think the answer must be d by option elimination but i don't really get the meaning of it.

http://sql-plsql.blogspot.in/2013/06/difference-candidate-composite-key.html

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