Data Independence for Data
Program #1 reserves space for the entire record (fields A to K). If the record format is changed, the space must be changed. Program #2 calls the DBMS to deliver just the fields it uses (D G H K). It still reserves space, but unless a field has been resized, it is not affected by other field changes. Program #3 is fully independent of the data structure. It calls for data by field name, and the DBMS allocates the space at runtime.
Data Independence for Processing
Program #1 uses a hard-coded value to test credit limit. To change the limit, the program must be recompiled. Program #2 retrieves the credit limit from a database. To change it, only the database must be updated, a simpler task.
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