• Table of Content

Chapter 5 The Relational Data Model and

Relational Database Constraints

Relational Model Concepts

Relational model represents the database as a collection of relations. A relation is nothing but a table of values.

Figure 5.1 The attributes and tuples of a relation STUDENT.

In the formal relational model terminology:

• A row is called a tuple, $t$.
• A column header is called an attribute, $A$.
• The number of attributes is called the degree, $n$.

The data type describing the types of values that can appear in each column is represented by a domain of possible values.

Domains, Attributes, Tuples, and Relations

A domain $D$ is a set of atomic values. By atomic we mean that each value in the domain is indivisible as far as the formal relational model is concerned.

• Example

A relational schema is denoted by,

$$ R(A_1, A_2, \dots, A_n) $$

where $R$ is the name of the relation and $A_i$ is the name of each attribute.

• Example

A relation $r$ of the relational schema is a set of of $n$-tuples,

$$ r = \{t_1, t_2, \dots, t_m\} $$

Each $n$-tuples $t$ is an ordered list of $n$ values,