Introduction to database management systems

Data independence is a form of database management which keeps data separated from all programs that make use of it. Data independence can be defined as the capacity to change schema  at  one level  without  changing  the  schema  at  next  higher  level.

Logical Data Independence

Logical data independence indicates that conceptual schema can be changed without affecting existing external schemas. The change would be absorbed by mapping between external and conceptual levels. Logical data independence also insulates application programs from operations such as combining two records into one or splitting an existing record into two or more records.

Physical Data Independence

Physical data independence indicates that physical storage structures or devices could be changed without affecting conceptual schema. The change would be absorbed by mapping between internal and conceptual levels. Physical data independence is achieved by presence of internal level of database and then, transformation from conceptual level of database to internal level.