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The sections that follow describe the EJB implementation process, and provide guidance for how to get an EJB up and running in WebLogic Server.

These sections discuss design options for WebLogic Server Enterprise Java Beans (EJBs), bean behaviors to consider during the design process, and recommended design patterns.Bean types vary in terms of the bean's relationship with its client. Some bean types stick with a client throughout a series of processes, serving as a sort of general contractor—acquiring and orchestrating services for the client. There are other bean types that act like subcontractors, they deliver the same single function to multiple client-oriented general contractor beans. A client-oriented bean keep track of client interactions and other information associated with the client process, throughout a client session—a capability referred to as maintaining state. Beans that deliver commodity services to multiple client-oriented beans do not maintain state. For a broad discussion of client interaction and state management, see J2EE and WebLogic Support for Service Types in Using WebLogic Server Clusters.

for read more information:
http://edocs.bea.com/wls/docs81/ejb/design_best_practices.html#1107234