Question

X →  Y holds on a schema k(K) if?

(a) At least one legal instance satisfies the functional dependency

(b) No legal instance satisfies the functional dependency

(c) Each and every legal instance satisfies the functional dependency

(d) None of the mentioned

I had been asked this question in unit test.

This intriguing question originated from Decomposition Using Functional Dependencies topic in portion Relational Database Design of RDBMS

Answer 1

The correct answer is (c) Each and every legal instance satisfies the functional dependency

Explanation: X →  Y holds on a schema k(K) if each and every legal instance satisfies the functional dependency. Even if one instance does not satisfy the functional dependency X→ Y does not hold on a schema.