Different between logical data independence and physical data independence.

Logical Data Independence	Physical Data Independence
Ability to change the logical (conceptual) schema without changing the external schema(user view)	Ability to change the physical schema without changing the logical schema
Modification is necessary whenever the logical structure of the database is altered	Modification are rarely done, as it is done to improve the performance of the database
It means we will be able to change the logical schema of the database without effecting the view level.	It means we will be able change the physical storage without affecting the logical level or view level.
It is more difficult to achieve.	It is relatively easy to achieve.
For example: Consider two users A & B, both are selecting the fields “employee_number”. If user B adds new column “salary” to the same table, it will not affect the user view level.	For example: Changing the storage drive of the data base form “C” drive to “D” drive will not affect the conceptual and view level as the new changes are absorbed by the mapping technique.