04 September 2009

The difference between logical and physical data independence

Logical data independence means that users are shielded from changes in the logical structure of the data, while physical data independence insulates users from changes in the physical storage of the data.


  1. 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.

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