Data independence means that “the application is independent of the storage structure and access strategy of data”. In other words, The ability to modify the schema definition in one level should not affect the schema definition in the next higher level.
Two types of Data Independence:
Physical Data Independence: Modification in physical level should not affect the logical level.
Logical Data Independence: Modification in logical level should affect the view level.
NOTE: Logical Data Independence is more difficult to achieve
What is a view? How it is related to data independence ?
A view may be thought of as a virtual table, that is, a table that does not really exist in its own right but is instead derived from one or more underlying base table. In other words, there is no stored file that direct represents the view instead a definition of view is stored in data dictionary.
Growth and restructuring of base tables is not reflected in views. Thus the view
can insulate users from the effects of restructuring and growth in the database. Hence accounts for logical data independence.
What is Data Model ?
A collection of conceptual tools for describing data, data relationships data semantics and constraints.
What is E-R model ?
This data model is based on real world that consists of basic objects called entities and of relationship among these objects. Entities are described in a database by a set of attributes.
What is Object Oriented model ?
This model is based on collection of objects. An object contains values stored in instance variables with in the object. An object also contains bodies of code that operate on the object. These bodies of code are called methods. Objects that contain same types of values and the same methods are grouped together into classes.
What is an Entity ?
It is a 'thing' in the real world with an independent existence.
What is an Entity type ?
It is a collection (set) of entities that have same attributes.
What is an Entity set ?
It is a collection of all entities of particular entity type in the database.
What is an Extension of entity type ?
The collections of entities of a particular entity type are grouped together into an entity set.
What is Weak Entity set ?
An entity set may not have sufficient attributes to form a primary key, and its primary key compromises of its partial key and primary key of its parent entity, then it is said to be Weak Entity set.