Access to business component for the view are directed through the business delegate to session facade which access the required business components. Although both business deligate and session facade access service locators and both belong to Business tier - Business delegate is more of a presentation interface to access business components through the session facade. The main purpose of BD is "You want to hide clients from the complexity of remote communication with business service components. " (from Core J2EE problem statement).Refer Business deligate. Hope this answers your question
Let's say you mail your resume/CV to a big company. The post office is like a business delegate business because it abstracts away the remoteness between you and the company... ok my analogy isn't perfect because you have to write the JNDI, er, address on the envelope and the post office might give you a RemoteException, er, Return to Sender - No Address Found. A real business delegate would know the address (or ask a service locator) and will usually wrap a RemoteException in a custom business exception.
OK, so the company received your resume/CV and it goes directly to HR because HR is the session facade. The HR rep will communicate with the IT departments, CEO, and whoever else needed in deciding whether to bring you in for an interview. Your resume/CV does NOT go directly to any other business components, er, employees! Not even if those people are needed to make the hiring decision! This is great because the other employees don't need to know how to be HR people in addition to their other duties. We keep a separation of concerns and so the resource manager only needs to know: "I need a good SCWCD programmer that understands business delegates and session facades!" And HR knows right where to find one.
Business Delegate is all about hiding the remoteness of the Objects/Components. Even if the components you are accessing are remote, but they appears to be local to you. And it does all this with the help of Service Locator (an another design patter) which in turn makes use of JNDI, RMI or other registeries.
And Session Fascade just adds an another layer between the interface and implementation to keep them seperate.