Explain dependency structures with example

Explain dependency structures with example.

Data independence is a fundamental form of transparency that we look for within a DBMS. Data definition occurs at two levels. At one level the logical structure of the data are specified and at the other level its physical structure.

The ability to modify a scheme definition in one level without affecting a scheme definition in a higher level is called data independence.

There are two kinds: Physical data independence and logical data independence

Physical data independence: The ability to modify the physical scheme without causing application programs to be rewritten. Modification at this level are usually to improve performance.

Logical data independence: The ability to modify the conceptual scheme without causing application programs to be rewritten. Usually done when logical structure of database is altered.

Logical data independence is harder to achieve as the application programs are usually heavily dependent on the logical structure of the data.

Fig. dependency structures