Let R = (A, B, C, D, E, F) be a relation scheme with the following functional…
1999
Let R = (A, B, C, D, E, F) be a relation scheme with the following functional dependencies:
C -> F, E -> A, EC -> D, A -> B
Which of the following is a key of R?
- A.
CD
- B.
EC
- C.
AE
- D.
AC
Attempted by 85 students.
Show answer & explanation
Correct answer: B
The correct answer is EC.
Attributes E and C do not appear on the right-hand side of any dependency, so every key must contain both E and C.
Now compute (EC)+:
Start with EC.
E -> A, so add A.
A -> B, so add B.
C -> F, so add F.
EC -> D, so add D.
Thus (EC)+ = {A, B, C, D, E, F}, which is the full set of attributes. Since neither E nor C can be removed, EC is a candidate key.