What Is DATA INDEPENDENCE? Also Describe Logical And Physical Data Independence?

The disjointing of data descriptions from the application programs (or user-interfaces) that uses the data is called data independence. Data independence is one o] the main advantages of DBMS. The three-schema architecture provides the concept of data independence, which means that upper-levels are unaffected by changes to lower-levels. The three schemas architecture makes it easier to achieve true data independence. There are two kinds of data independence.
(I)        Logical data independence (ii)      Physical data independence

Logical Data Independence:
Logical data independence is the ability to modify the conceptual schema without having alteration in external schemas or application programs. Alterations in the conceptual schema may include addition or deletion of fresh entities, attributes or relationships and should be possible without having alteration to existing external schemas or having to rewrite application programs.
Physical Data Independence:
Physical data independence is the ability to modify the inner schema without having alteration to the conceptual schemas or application programs. Alteration in the internal schema might include.
*  Using new storage devices.
*  Using different data structures.
*  Switching from one access method to another.
*  Using different file organizations or storage structures.
*  Modifying indexes.
The above-mentioned changes should be possible without having to change the conceptual or external schemas.

We can define data independence as the capacity to change the schema at one level of a database system in such a way that, the schema at next higher level needs not to be changed. There are two types of data independence. Which are given below.

Logical Data independence: It says that it is the capacity to change the conceptual schema in such a way that external schema will not need to change. To expand database, we can do changes in conceptual schema and we can also change conceptual schema to change constraints. It means that logical data independence gives us the freedom of changing the conceptual schema without worrying about external schema.

Physical Data independence: We can define it as it is the capacity to change the internal schema in such a way that we the conceptual schema will not need to be change. Changes in internal schema may be necessary because we may have to change some physical files. Data independence occurs because when the schema is changed at some level, the schema at the next higher level remains unchanged. However, only the mapping between the two levels is changed. During compilation or execution of a query, these two levels of mappings create an overhead.

Logical Data Independence:

Logical data independence is the ability to modify the conceptual schema without having alteration in external schemas or application programs. Alterations in the conceptual schema may include addition or deletion of fresh entities, attributes or relationships and should be possible without having alteration to existing external schemas or having to rewrite application programs.

Physical Data Independence:

Physical data independence is the ability to modify the inner schema without having alteration to the conceptual schemas or application programs. Alteration in the internal schema might include.
* Using new storage devices.
* Using different data structures.
* Switching from one access method to another.
* Using different file organizations or storage structures.
* Modifying indexes.