Which normalization form requires every functional dependency to be on a superkey?

Which normalization form requires every functional dependency to be on a superkey?

• A. BCNF (Boyce-Codd Normal Form)
• B. 3NF (Third Normal Form)
• C. 4NF (Fourth Normal Form)
• D. 2NF (Second Normal Form)

Answer: (A)

The form being described enforces that the determinant of every nontrivial functional dependency must be a superkey. A superkey uniquely identifies all attributes of the relation, so when X -> Y holds with X as a superkey, any change to X won’t leave Y in an inconsistent state and the design avoids update anomalies more rigorously. This makes it stricter than other normal forms. For example, a dependency where a non-key attribute determines another attribute would not fit this form, because the left side isn’t a superkey. A classic illustration is a relation with attributes A, B, C where A -> B and B -> C hold; A is a key (A+ includes all attributes), but B is not a key (B+ doesn’t include A). The B -> C dependency thus violates BCNF and would lead to decomposing the relation into BCNF-compliant pieces. In comparison, third normal form allows certain dependencies with a non-superkey left side if the right side is a prime attribute, so it’s looser than BCNF. Fourth normal form deals with multivalued dependencies, and second normal form focuses on removing partial dependencies of non-prime attributes on candidate keys, neither of which requires every functional dependency to have a superkey on the left.

The form being described enforces that the determinant of every nontrivial functional dependency must be a superkey. A superkey uniquely identifies all attributes of the relation, so when X -> Y holds with X as a superkey, any change to X won’t leave Y in an inconsistent state and the design avoids update anomalies more rigorously.

This makes it stricter than other normal forms. For example, a dependency where a non-key attribute determines another attribute would not fit this form, because the left side isn’t a superkey. A classic illustration is a relation with attributes A, B, C where A -> B and B -> C hold; A is a key (A+ includes all attributes), but B is not a key (B+ doesn’t include A). The B -> C dependency thus violates BCNF and would lead to decomposing the relation into BCNF-compliant pieces.

In comparison, third normal form allows certain dependencies with a non-superkey left side if the right side is a prime attribute, so it’s looser than BCNF. Fourth normal form deals with multivalued dependencies, and second normal form focuses on removing partial dependencies of non-prime attributes on candidate keys, neither of which requires every functional dependency to have a superkey on the left.