What is Data Independence in Database
1) An ability to modify a schema definition in one level without affecting a schema
definition in a higher level is called data independence .
2) If any change occur ¡n the schema of lower level, the upper levels are unaffected,
this is called data independence.
3) The Database management system is defined in three level architecture: External’
Schemas (users view), Conceptual Schema, and Internal Schema or Physical
4) There are two kinds of data independence
a. Logical data independence
b. Physical data independence
Logical Data Independence:
1) An ability to modify the conceptual schema without causing application program
to be changed or rewritten.
2) Modifications at this level are usually to improve performance.
3) User may alter the conceptual schema by combining two records into one,
splitting an existing record into two or by adding new record type, by remove
records type etc.
4) Logical data independence is harder to achieve as the application programs
usually heavily dependent on the logical structure of the data.
Physical Data Independence:
1) An ability to modify the physical schema (Internal Schema) without have
alteration to the conceptual schemas or application program.
2J Modifications at this level are usually to improve performance.
3) If there is a need for change of physical device or file organization to upgrade
new technology, it should not affect the logical schema.
4) For example, in case we want to change or upgrade the storage System itself anti
want to replace storage device to some other means of storage, it should not have
any impact the logical schema.