DBMS - data independence

               DATA INDEPENDENCE

Any software has mainly two parts, first is the database and second is the application or program which accesses and uses the database. First the database is designed and then the application program are written for it, which heavily depends on database design. sometimes, after the application program has been written there is need to change the storage structure or database design. data independence is all about, the ability to modify a schema definition (i.e. storage structure) in one level without affecting a schema definition in the next higher level.

 There are two levels of data independence.

1. physical data independence : physical data independence is the ability to modify the physical schema without causing application programs to be written.

2.logical data independence : logical data independence is the ability to modify logical schema without causing application programs to be rewritten.

modification at the logical level are necessary whenever the logical structure of the database is altered.

logical data independence is more difficult to achieve than is physical data independence, since application programs are heavily dependent on the logical structure of the data that they access.

the concept of data independence is to hide implementation details from users & helps the users  to concentrate on the general structure, rather than on low-level implementation details.