Data Independence

1. The ability to modify a scheme definition in one level without affecting a scheme definition in a higher level is called data independence.

2. There are two kinds:
   • Physical data independence
     • The ability to modify the physical scheme without causing application programs to be rewritten
     • Modifications at this level are usually to improve performance
   • Logical data independence
     • The ability to modify the conceptual scheme without causing application programs to be rewritten
     • Usually done when logical structure of database is altered
3. Logical data independence is harder to achieve as the application programs are usually heavily dependent on the logical structure of the data. An analogy is made to abstract data types in programming languages.