Some Important Placement Questions of DBMS#1

Some Important Placement Questions of DBMS

1. What is Data Independence in DBMS?

Data independence means that "the application is independent of the storage structure & 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

2. What is a view in DBMS? 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 & restructuring of base tables is not reflected in views. Thus the view 136 can insulate users from the effects of restructuring & growth in the database. Henceaccounts for logical data independence.

3. What is Data Model in DBMS?

A collection of conceptual tools for describing data, data relationships data semantics & constraints.

4. What is E-R model?

This data model is based on real world that consists of basic objects called entities & of relationship among these objects. Entities are described in a database by a set of attributes.

5. 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 & the same methods are grouped together into classes.