What is Relational Model?

The relational model is a simple and powerful data model proposed by E. F. Codd in 1970. It represents data in the form of tables (relations) and uses a mathematical concept of relations from set theory. In this model, data is organized into rows and columns, where each row represents a tuple and each column represents an attribute.

Features of Relational Model

• Data is stored in tables (relations).
• Each table has a unique name.
• Each row represents a tuple (record).
• Each column represents an attribute (field).
• Values in a column are from the same domain (data type).
• Uses primary key to uniquely identify a tuple.
• Supports relational algebra and SQL for data manipulation.
• Provides data independence and reduces data redundancy.

Structure of a Relation

In the Relational Model of a Database, a relation is represented as a two-dimensional table consisting of rows and columns. Each relation stores information about a particular entity, such as Student, Employee, Course, Department, Product, etc.The main components of the structure of a relation are tuples, attributes, domains, degree, and cardinality.

• Tuples (Rows): Each row represents a single record or entity.
• Attributes (Columns): Each column represents a property of the entity.
• Domain: Set of allowed values for each attribute.
• Degree: Number of attributes in a relation.
• Cardinality: Number of tuples (rows) in a relation.

For example, consider the following Student relation:

In the above Student relation,

Degree = 4 (ID, Name, Class, Age)

Cardinality = 3 (3 tuples / rows)

Relational Constraints

Relational constraints are rules applied to the data in a relational database to maintain accuracy, consistency, validity, and integrity of the data.They prevent incorrect, duplicate, or meaningless data from being entered into the database.

1. Domain Constraint :A domain constraint specifies that an attribute can contain only values from its defined domain.For example, consider a Student table:

2.Entity Constraints 

Entity constraints are rules that ensure that every row (tuple) in a relation can be uniquely identified and that important key values are not missing.The main entity constraint is the Entity Integrity Constraint.Entity constraint means that every record in a table must have a unique identification number.