Concept of Database || DBMS

Concept of Database 

 As a database may be viewed through three levels of abstraction, any change at a level may affect other level's schemes. Since the Database keeps on growing there may be frequent changes at times. This should not lead to the redesigning and reimplementation of the database. The concept of data independence proves beneficial in such a context.
There are two levels of Data independence
1.Physical
2.Logical

Physical Data Independence
Physical Data independence refers to the ability to modify the scheme followed at the physical level without affecting the scheme followed at the conceptual level. That is the application programs remain the same even though the scheme at the physical level gets modified. Modifications at the physical level are occasionally necessary in order to improve the performance of the system.

Logical Data Independence
Logical Data Independence refers to the ability to modify the conceptual scheme without causing any changes in the scheme followed at view levels. The logical data independence ensures that the application programs remain the same. Modifications at the conceptual level are necessary whenever logical  structures od the database get altered because of some unavoidable reasons
For example, the introduction of paternity leaves in the employee database for the first time.  
In more difficult to achieve logical data independence than the physical data independence. The reason being that the apllication programs are heavily dependent on on the Logical Structure of the database.
The abstract data types in modern programming languages implement the concept of data independence to a large extent. Both hide implementation details from the users. This allows users to concentrate on the general structure rather than low-level implementation Detail.