Physical Data Independence vs Logical Data Independence in Database

Physical Data Independence vs Logical Data Independence in Database

 Data Independence

A major purpose of a database system is to provide the users with an abstract view of data. To hide the complexity from users database apply different levels of abstraction. The following are different levels of abstraction.

Physical Level
Logical Level
View Level 

Physical Level
Physical Level is the lowest level of abstraction and it defines the storage structure.The physical level describes complex low level data structures in detail.The database system hides many of the lowest level storage details from the database programmers. Database Administrators may be aware of certain details of physical organization of data.

Logical Level
This is the next higher level of abstraction which describe what data are stored in database, relation between data, types of data etc . Database programmers, DBA etc knows the logical structure of data

View Level
This the highest level of abstraction. It provides different view to different users. At the view level users see a set of application programs that hide details of data types. The details such as data type etc are not available at this level. Only view or Access is given to a part of data according to the users access right

Physical Data Independence
 
The changes in physical Level does not affect or visible at the logical level.The logical schema remain unchanged eventhough there is change in the internal schema at the physical level. This is called physical data independence.The physical level deals with the storage structure where as logical level deals with logical schema.

Logical Data Independence
 
The changes in the logical schema will not be visible or affect at the view level.The view level schema remain unchanged eventhough there is change in the schema  at the logical level. This is called logical data independence