DATA INDEPENDENCY-DAY6

Data Independence

The ability to modify a scheme definition at one level without affecting the scheme at the next higher level

Physical data independence

The ability to change the physical scheme without affecting the conceptual scheme

Logical data independence

The ability to change the conceptual scheme without affecting sub-schemes

· Easy if information is added to the conceptual scheme

· Often impossible if information used in some sub-scheme is deleted from the conceptual scheme

Notes:

· Physical data independence implies that programs that use the conceptual level are unaffected by changes to the physical scheme

· Logical data independence implies that programs that use some sub-scheme are unaffected by changes to the conceptual scheme

· Data independence is like data abstraction in software engineering