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Data Independence


As the database grow, the overall logicalstructure of the data becomes complex. To change the data in the database without forcing a change in the application programs which use that database, two levels of independence are required :

Logical Data Independence :
The overall logical structure of the data may be changed without changing the application programs

Physical Data Independence :
The physical layout and organization of the data may be changed without changing either the overall logical structure of the data or the application programs.
application programs are independent of the format of the data, access methods and the location of the data.

As an example... assume the following records structure:
HumanResources-Record : {emp-num, emp-name}
Finance-Records : {emp-num, basic-pay, DA}
Administration-Record : {emp-num, emp-work-days}

Also assume that there are corresponding appliations as follows :
HumanResources-Application : [provides details about the emp-num, emp-name and basic-pay] and
Finance-Application : [emp-num, emp-name, basic-pay and DA]

following data indepence concept, if a field HRA is added to the Finance-Record, it should nto affect HumanResources-Application and Finance-Application

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