Rules for EJB Application

Question

Hello,
I am developing an ejb application. I am still learning and this is my first application.
1) I am unable to understand where should use Entity Beans or session bean and why i mean how i justify my using Entity bean or session bean? If using entity beans how to decide that it should be BMP or CMP and why? how i justify using CMP or BMP?
2) I have heard that Entity beans are related to Persistant data if so then if some application design has 50 to 75 tables then should there be those many Entity Beans corresponing to those tables? if i use 50 to 75 entity beans then what effect will it have on performance??
it will be a great help if someone solve these queries by giving proper example. suppose in context a web application where vendors post there porduct to sell and different users come and purchase these products online.
Thanxs

Answer 1

Use session beans for business logic components and Entity beans for accessing persistent data. It is a common pattern to put up a "session facade" over the entity beans so that the client doesn't have to assume anything about storage and retrieval of data. You can have a 1-1 mapping between entity beans and database tables, but you don't have to. Read the online "Mastering EJB" book at www.theserverside.com to better understand the concept of EJB's.