GATE 2013 CS (CS1) – Question 64
R(A,B,C,D,E,F,G,H) has atomic fields. Exactly the dependencies implied by F={CH→G,A→BC,B→CFH,E→A,F→EG} hold. How many candidate keys exist?
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Correct answer: (B) 4
Explanation
D never appears on a right-hand side, so every key must include D. Each of A,B,E,F determines the other three and C,G,H through the given chain, so AD,BD,ED,FD are keys. No combination using only C,G,H,D can derive A,B,E,F. These four are all the minimal keys, B.