What does a functional dependency X -> Y mean?

What does a functional dependency X -> Y mean?

• A. Y depends on X
• B. X depends on Y
• C. X and Y are independent
• D. X and Y are the same attribute

Answer: (B)

A functional dependency X -> Y means Y is determined by X: if two records have the same X value, their Y values must be identical. In other words, X carries enough information to fix Y. So the description that matches this idea is that Y depends on X. The other interpretations don’t fit: saying X depends on Y reverses the relationship, claiming X and Y are independent ignores the dependency, and saying X and Y are the same attribute confuses dependency with equality.

A functional dependency X -> Y means Y is determined by X: if two records have the same X value, their Y values must be identical. In other words, X carries enough information to fix Y.

So the description that matches this idea is that Y depends on X. The other interpretations don’t fit: saying X depends on Y reverses the relationship, claiming X and Y are independent ignores the dependency, and saying X and Y are the same attribute confuses dependency with equality.