Consider the schema R = (S, T, U, V) and the functional dependencies S→T, T→U,…
1999
Consider the schema R = (S, T, U, V) and the functional dependencies S→T, T→U, U→V and V→S. The relation R is:
- A.
Not in 2NF
- B.
In 2NF but not in 3NF
- C.
In 3NF but not in 2NF
- D.
In both 2NF and 3NF
Attempted by 83 students.
Show answer & explanation
Correct answer: D
The correct answer is: In both 2NF and 3NF.
Compute the closures using the given functional dependencies:
S+ = {S, T, U, V}
T+ = {T, U, V, S}
U+ = {U, V, S, T}
V+ = {V, S, T, U}
Thus S, T, U and V are all candidate keys. Every non-trivial dependency has a candidate key on its left-hand side, so the relation is actually in BCNF.
Since BCNF implies 3NF, and 3NF implies 2NF for this classification, R is in both 2NF and 3NF.