A database system provides two types of data independence.
- Logical data independence.
- Physical data independence.
Logical data Independence
When a user tries to access some data, she is not concerned about what is the logical representation of data items in the database. Rather the user’s concern is the view of data that is provided and whether the data is directly usable.
Database system ensures that the user’s view of data is independent of the logical representation of data in the database. Such independence is of great importance to user applications. Because if the dependency exists, any change to the logical representation would require a code level change of the user application, which is often painful. Logical data independence avoids this issue.
Scenario : A new column is added to the logical schema. Applications remain unaffected.
Physical data Independence
Logical schema of database is created from the physical data. Physical data independence suggests that any changes in physical organisation of data should not affect the logical schema of database.
Scenario : The storage data structure is updated to use a B* tree instead of partitioned lists. This does not affect the columns in logical schema.