Session object can be used for storing session-specific 
information that needs to be maintained between server 
round trips and between requests for pages.various modes of 
storing ASP.NET session is:InProc,StateServer,and SQL 
SERVER state.

          Abstract classes provide a simple and easy way to 
version your components. By updating the base class, all 
inheriting classes are automatically updated with the 
change. Interfaces, on the other hand, cannot be changed 
once created. If a new version of an interface is required, 
you must create a whole new interface.
            If we want to provide common, implemented 
functionality among all implementations of your component, 
use an abstract class. Abstract classes allow you to 
partially implement your class, whereas interfaces contain 
no implementation for any members.

       Inheritance is getting properties from parent class 
to child class.

session are maintain on the server,session are created for
the individual user,the data are stored in the session
butare secured,

all methods are abstract method in the interface,and we can
not use any modifier before method in interface calsses.
Abstact class having abstract method as well as user defind
method,