Relational Data Model in DBMS: An Introduction

 

Relational Model:

 

The relational model represents data and relationships among data by a collection of tables, each of which has a number of columns with unique names. In a relational model the database is organized in fixed format.

 

Following figure shows a sample relational table. it consists of two tables, one is the employee information table and the other is the salary table for the particular employee information table.

 

Emp_Id	Emp_name	Emp_add	Emp_dept
101	Ajay	Wardha	Computer
102	Vijay	Nagpur	Mechanical
103	Sujay	Amravati	Civil

 

Fig: Employee information table

 

Emp_Id	Salary
101	30000
102	25000
103	20000

 

Fig: salary table

 

 

The properties of relational tables are as follows:

 

1.    Values are atomic.

 

2.    Each row is unique.

 

3.    Column values are of the same type.

 

4.    The sequences of columns are not important.

 

5.    The sequences of rows are also not important.

 

 

·      In a relational table, each column has a unique name.

 

·     Certain fields may be designated as keys which mean that searches for specific values of that field will use indexing to speed them up where fields in two different tables take values from the same set, a join operation can be performed to select related records in the two tables by matching values in those fields.

 

·      Often, but not always, the fields will have the same name in both table.

 

·      In above ex: the attribute Emp_ID can be a key (maybe a primary key) which can be indexed or sorted in an order to search specific value for Emp_ID.