session beans are function beans.two types of session beans 
are stateless & stateful.It is not persitent on three cases
 1. server crash
 2. server shutdown
 3. time out

where as entity beans are value beans. it contains only 
setter and getter methods.it is persistent bean.it 
maintains database, for storing objects. two types of 
entity bean are 
bean managed persistance & container managed persistance