ENTITY BEANS: it provide object representaion of data in the database. they can allow shared access from multiple user.
SESSION BEAN: represent a process excecutiong on the behalf of a single object.even though it does not present directly shared data . it can access or update the data in the database . session bean can be ststeful or stateless. a session beans retains the conversational state of the client acrosss multiple method calls. stateless session bean are dedicated to the client only for the duration of single method call
message driven bean: are asynchronously invokes when a client message arrives. client never call them directly. so they do not have any home or component interface