Chapter 5, Problem 1RQ

To determine

Defining functional dependency (Dependence).

Explanation of Solution

The functional dependency is a relationship between two attributes, generally between primary key and other non-key attributes within a table.

Consider a relation R where the attribute B is functionally dependent on the attribute A (usually the primary key).

It can be written as follows:

$\text{A}\to \text{B}$

The left side in the above relation is called as the determinant and the right side is known as the dependent (Functional dependency). If A can determine the value of B then it means that if value of A is knowing one get the value of B without ambiguity.

For Example, consider a table with attributes StudentID, Name, Class, DateOfBirth where the StudentID (Primary key) determines the Name, Class and DateOfBirth :

$\underset{\_}{\text{StudentID}}\to \text{Name,Class,DateOfBirth}$

StudentID	Name	Class	DateOfBirth
001	Chris	5	09/11/2011
002	David	6	02/02/2010
003	Johana	7	08/05/2011

Table 1

Table 1 shows the key attribute that is StudentID, which determines the Name, Class and DateOfBirth.

$\begin{array}{l}\underset{\_}{\text{StudentID}}\to \text{Name}\\ \underset{\_}{\text{StudentID}}\to \text{Class}\\ \underset{\_}{\text{StudentID}}\to \text{DateOfBirth}\end{array}$