Question

difference between logical data independence & physical data independence?

Answer 1

Physical data independence is the ability to modify the physical schema without making it necessary to rewrite application programs. E.G., changing from unblocked to blocked record storage, or from sequential to random-access files.

Logical data independence is the ability to modify the conceptual schema without making it necessary to rewrite application programs. E.G., adding a new field to a record. An application program’s view hides this change from the program.

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Answer 2

LOGICAL DATA INDEPENDENCE:

Conceptual schema can be changed without affecting external schema

We change/modify conceptual schema when structure of database is altered
It is very difficult because, we have to see that the relationship must not changing, data is not getting lost and some other factors

It only provide immunity to external schema and application programs


PHYSICAL DATA INDEPENDENCE:


physical storage structure or devices can be changed without affecting conceptual schema

Modification are performed to improve performance

It is not difficult because, we have to only replace the data from one device to another device. No need to change the data only change the location of data

It provide independence and immunity to conceptual and external schema