This week's book giveaway is in the OCMJEA forum. We're giving away four copies of OCM Java EE 6 Enterprise Architect Exam Guide and have Paul Allen & Joseph Bambara on-line! See this thread for details.
The way you have your objects defined you are expecting to a customer to have one address and that address to belong to exactly one Customer. But the way you are attempting to use it you are saying that one address can have many customers. With the way you have it defined you must define 2 Addresses with their own unique persistent ids even if they are both "ABCStreet"