INTEGRITY RULES IN DBMS

Integrity  Rules:

Database Management System  provides  high level of data integrity, by using the  Integrity Rules:

1. Entity Integrity: Entity integrity says that  a prime attribute in a relation cannot accept null values or duplicate value.

2. Referential Integrity: The referential integrity rule is related along with the foreign key concept. Let R1 and R2 are two relations where R1 is having an attribute(s) with primary key. Let R2 be having a foreign key, that refers to relation R1 via the same set of attributes. Then the value of the foreign key in a tuple in R2 relation must either be equal to primary key of a tuple in a relation R1 relation or be entirely NULL.

R1

Department_ID	Department_Name	Department_Head	Department_Addres
D1	HR	Jacob	London
D2	IT	Rohan	Newyork
D3	FINANCE	Michel	Delhi

R2

EMP_ID	EMP_Name	EMP_City	Department_ID
E1	Rohan		D2
E2	Mukesh		D1
E3	Joseph		D1
E4	Ron		D1
E5	Michel		D3
E6	Jacob		D1

In above example  , in relation R1  Department_ID  is primary key  where as in R2 Department_ID is foreign key.

Value of the foreign key in R2 is same as Value exist in R1 of primary key.