Q13,paper 2, D 12.Which of the following is true ?

(A) A relation in BCNF is always in 3NF.
(B) A relation in 3NF is always in BCNF.
(C) BCNF and 3NF are same.
(D) A relation in BCNF is not in 3NF.
Answer (A)
A relation is in Boyce codd normal form, if for every functional dependency X->Y in a set of functional dependency, either of them hold.
• X is super key of R.
Or
• Y is a subset of X.
Three NF is little bit relaxed which can be understood by the following definition of 3NF.
A relation is in 3NF if for every functional dependency X->Y in a set of functional dependency either of them hold.
• X is super key of R.
Or
• Y is a subset of X.
Or • Y is a subset of K for some key of R.