UGC-NET | UGC NET CS 2015 Dec – II | Question 20

A relation R = {A, B, C, D, E, F,G} is given with following set of functional dependencies:
F = {AD → E, BE → F, B → C, AF → G}
Which of the following is a candidate key ?

(A) A
(B) AB
(C) ABC
(D) ABD

Answer: (D)
Explanation: [AD]⁺ = ADE.
[BE]⁺ = BCEF.
[B]⁺ = BC.
[AF]⁺ = AFG.
Nothing drives all the attributes, but if We add B in first key i.e. [ADB] then it will give all the attribute [ADB]⁺ = ABCDEFG.
So, option (D) is correct.

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