BCNF is not used for cases where a relation has
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
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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