GATE | GATE-CS-2002 | Question 50

From the following instance of a relation scheme R (A, B, C), we can conclude that :

A B C
1 1 1
1 1 0
2 3 2
2 3 2

(A) A functionally determines B and B function­ally determines C

(B) A functionally determines B and B does not functionally determine C
(C) B does not functionally determine C
(D) A does not functionally determine B and B does not functionally determine C


Answer: (C)

Explanation: Generally Normalization is done on the schema itself.



From the relational instance given,we may strike out FD s that do not hold.

e.g.B does not functionally determine C(This is true).

But we cannot say that A functionally determines B for the entire relation itself. This is because that, A->B holds for this instance, but in future there might be some tuples added to the instance that may violate A->B.

So overall on the relation we cannot conclude that A->B, from the relational instance which is just a subset of an entire relation.

Refer http://quiz.geeksforgeeks.org/database-normalization-introduction/ for more details.

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