A view may be thought of as a virtual table, that is, a table that does not really exist in its own right but is instead derived from one or more underlying base table. In other words, there is no stored file that direct represents the view instead a definition of view is stored in data dictionary.

Growth and restructuring of base tables is not reflected in views. Thus the view can insulate users from the effects of restructuring and growth in the database. Hence accounts for logical data independence.

Extension -It is the number of tuples present in a table at any instance. This is time dependent.

Intension -It is a constant value that gives the name, structure of table and the constraints laid on it.

 Redundancy is controlled.
 Unauthorised access is restricted.
 Providing multiple user interfaces.
 Enforcing integrity constraints.
 Providing backup and recovery.

There are two Integrity rules. Entity Integrity: States that "Primary key cannot have NULL value"
Referential Integrity: States that "Foreign Key can be either a NULL value or should be Primary Key value of other relation.