• Table of Contents

Chapter 14 Basics of Functional Dependencies and Normalization for Relational Databases

When designing a relational database schema, there are several schemas are possible:

• Some are better and convenient.
• Some are bad and not desirable.

Relational database design ultimately produces a set of relations. The implicit goals of the design activity are information preservation and minimum redundancy.

Functional Dependencies

A functional dependency (or FD for short), denoted by,

$$ X \to Y $$

expresses semantic information on two set of attributes, $X$ and $Y$. We can say:

• $X$ functionally determines $Y$.
• $Y$ is functionally dependent on $X$.

A functional dependency is a property of the relation schema $R$. Consider the following table of data of the relational schema $R(A, B, C, D)$.

Figure 14.1 A relation $R(A, B, C, D)$ with its extension.

For the following figure, the following FDs may hold:

1. $B \to C$
2. $C \to B$
3. $\{A,B\} \to C$
4. $\{A,B\} \to D$