Data Independence

Data independence is ability to modify a schema definition in one level without affecting a schema definition in the next higher level.

There are two levels of data independence:

1. Physical Data Independence
2. Logical Data Independence

These are described below:

1. Physical Data Independence:

• Physical Data Independence is the ability to modify the physical schema without requiring any change in application programs.
• Modifications at the internal levels are occasionally necessary to improve performance. possible modifications at internal levels are change in file structures, compression techniques, hashing algorithms, storage devices, etc.
• Physical data independence separates conceptual levels from the internal levels.
• This allows to provide a logical description of the database without the need to specify physical structures.
• Comparatively, it is easy to achieve physical data independence.

2. Logical Data Independence:

• Logical data independence is ability to modify the conceptual schema without requiring any change in application programs.
• Modification at the logical levels are necessary whenever the logical structures of the database is altered.
• Logical data independence separates external level from the conceptual view.
• Comparatively it is difficult to achieve logical data independence.
• Application programs are heavily dependent on logical structures of the data they access.so any change in logical structure also requires programs to change.

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