It is acceptable, since your facade decouples your client from complex relationships between low-level business objects (your ShoppingCart-bean,your CreditCard Processing-bean,and your entity beans). This would also reduce the number of network calls from the client, which are the problems this Design pattern solves.
Your session facade could either be a stateful or a stateless session bean.
You cannot implement an entity bean as a session facade, however you have the composite entity design pattern which allows you to implement an entity bean as a facade to manage other entities (persistent objects). This also reduces the number of network calls from the client side, since you must not implement every persitent object as an entity bean (assuming you are using
EJB 1.1 or lower version).
Ebage
SCJP SCEA [ July 28, 2003: Message edited by: Christian Ebage ]