Explain the difference between the logical and physical data independence?

Data independence is the capacity to change the schema at one level of database system without having to change the schema at the next higher level. Physical data independence refers to the ability to modify the internal schema without having to change the conceptual or external schemas. That is the application programs remain the same even though the schema to physical level gets modified. Modifications at the physical level are occasionally necessary to improve the performance of the system.

Logical data independence refers to the ability to modify the conceptual schema without having to change external schema or applications programs. 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 modified because of some unavoidable reasons.