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Data independence is the ability to change the schema at one level of the database system without having to change the schema at the other levels. Data independence is of two types, namely, logical data independence and physical data independence.

Logical data independence:

It is the ability to change the conceptual schema without affecting the external schemas or application programs. The conceptual schema may be changed due to change in constraints or addition of new data items or removal of existing data items, etc. from the database. The separation of the external level from the conceptual level enables the users to make changes at the conceptual level without affecting the external level or the application programs.

Physical data independence:

It is the ability to change the internal schema without affecting the conceptual or external schema. An internal schema may be changed due to several reasons such as for creating additional access structure, changing the storage structure, etc. The separation of internal schema from the conceptual schema facilitates physical data independence.

Logical data independence is more difficult to achieve than the physical data independence because the application programs are always dependent on the logical structure of the database.

Importance: Data independence is an important characteristic of DBMS as it allows changing the structure of the database without making any changes in the application programs that use the database.

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