Data Abstraction : Why & levels

A DBMS is a collection of interrelated data and a set of programs that allows users to access the data and modify the data.

A purpose of a DBMS is to provide the users with an abstract view of
data so for that proposed system hides certain details of how the data
is stored and maintained.

For the system is to usable it must retrieve data efficiently.This
concern led to the design of complex data structures for the
representation of data in the database.

Since many database users are not computer trained , developers hide
the complexity from users through different levels of abstraction to
simplify users interaction with the system.

1.Internal Level ( Physical Level ) :- It is
the one closest to the physical storage devices.It describes how data
are actually stored on the storage medium such as hard disk , magnetic
tapes etc.

2.Logical Level :- It describes what data are
stored in the database and what relationships exists among the data.The
entire database is described in terms of a small structures.This level
is used by the DBA who must decide what information is to be kept is the

3.View Level ( External Level ) :- The
highest level of abstraction describes only a part of the entire
database. Despite the use of the simple structures at the logical level ,
some complexity remains due to the large size of the database.The
System may provide different views for same database.

Pawan Kumar