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Relational Model Concept in DBMS

Relational Model Concept

Relational model refers to any table with rows and columns. Each row of the table is called a tuple, and each column has a name, also known as an attribute.

Domain: It consists of some atomic values of a particular attribute.

Attribute: It is the name given to a particular column in a table. Each attribute Ai is required to have a domain, dom(Ai).

Relation instance: The relation instance constitutes of a limited set of tuples in the relational database system. There are no duplicate tuples in relation instances.

Relational schema: The relation name and columns names are present in a relational schema.

Relational key: All rows have either one or more than one attributes in the relational key. It is useful in identifying the rows in the relation.

Example: EMPLOYEE Relation

Employee ID

Name

Phone

Designation

Work Experience

145

Rohit

8981726920

HR

1 year

123

Sameer

7868273674

Manager

3 years

178

Neha

9282738489

Personal Secretary

6 months

134

Ravi

9872628393

Editor

2 years

123

Asha

9873637288

Engineer

2 years

 

  • In the table given above, Employee ID, Name, Phone, Designation, and Work Experience are the attributes for a given column.
  • The instance of schema EMPLOYEE consists of 5 tuples.
  • t2= <123, Sameer, 7868273674, Manager, 3 years>

 

Features of Relation

  • Name of the relation is different from all other relations.
  • There is only one atomic value in each relation cell.
  • There is a distinct name given to each attribute.
  • There is no significance of the attribute domain.
  • No duplicate value is there for any tuple.
  • A different sequence can be used for the order of tuple.
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