Question

Let $P, Q, R, S$ be relational schemas. Let ``$\rightarrow$'' indicate a functional dependency (FD) in this context. Which of the following best describes the meaning of a functional dependency?

• A. if then or
• B. if then
• C. if then
• D. if and then

Hint:

Always remember: A functional dependency $X \rightarrow Y$ means \textbf{``$X$ uniquely determines $Y$''} or \textbf{``If $X$, then $Y$''}. It is a logical implication, not an AND/OR relationship.

Answer 1

The Correct Option is B

Step 1: Recall the definition of a functional dependency.
In relational database theory, a functional dependency $X \rightarrow Y$ means:
If two tuples have the same values for attribute set $X$, then they must have the same values for attribute set $Y$.
Step 2: Interpret the logical meaning.
The statement $X \rightarrow Y$ is logically read as:
``If $X$ holds, then $Y$ must hold.''
It does not mean logical conjunction (AND), nor does it involve alternatives (OR).
Step 3: Analyze the options.
(a) if then or: This introduces an unnecessary logical OR. Incorrect.
(b) if then: Correct interpretation of a functional dependency.
(c) if then: Duplicate wording, but option (b) is the standard correct choice.
(d) if and then: Incorrect logical structure; functional dependency is not conjunctive.
Step 4: Conclusion.
A functional dependency in a relational schema is correctly interpreted as: \[ \boxed{\text{if then}} \]