The ability to modify a schema definition in one level without affecting a scheme definition in the next higher level is called DATA INDEPENDENCE
- Physical Data Independence
- It refers to the ability to modify the scheme followed at the physical level without affecting the scheme followed at the conceptual level.
- The application programs remain the same even though the scheme at the physical level gets modified.
- Modifications at the physical level are occasionally necessary in order to improve performance of the system.
- Logical Data Independence
- It refers to the ability to modify the conceptual scheme without causing any changes in the schemes followed at view levels.
- The logical data independence ensures that the application programs remain the same.
- Modifications at the conceptual level are necessary whenever logical structures of the database get altered because of some unavoidable reasons.
It is more difficult to achieve logical data independence than the physical data independence.
The reason being that the application programs are heavily dependent on the logical structure of the database.