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
schema
(storage).
What Is DataBase and How To Use
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.
What are the components of database system
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.