Explain the difference between physical and logical data independence?
In Logical Data Independence the logical schema is modified without rewriting the application programs whereas in Physical Data Independence the physical schema is changed without rewriting the application programs.
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Logica Data Independence Physical Data Independence Logical Data Independence is mainly concerned with the structure or changing the data definition. Mainly concerned with the storage of the data. It is difficult as the retrieving of data is mainly dependent on the logical structure of data. It is easy to retrieve. Compared to Logic Physical independence it is difficult to achieve logical data independence. Compared to Logical Independence it is easy to achieve physical data independence. You need to make changes in the Application program if new fields are added or deleted from the database. A change in the physical level usually does not need change at the Application program level. Modification at the logical levels is significant whenever the logical structures of the database are changed. Modifications made at the internal levels may or may not be needed to improve the performance of the structure. Concerned with conceptual schema Concerned with internal schema Example: Add/Modify/Delete a new attribute Example: change in compression techniques, hashing algorithms, storage devices, etc