Class diagrams?

Hello folks,
Could there be a class diagram where no relationship between the domain objects? I mean, it seems screwed, but assuming you get data from 3 different remote systems, let�s say one about User preferences, another content and the third bill the user. These are somehow related, sure, but are not directly linked. U can think of it as 3 tables (in 3 diff systems) where the information you get from the first (via user ID) will be the primary key in the second table (preferences to take content) and according to this content u charge him? Does it give any sense to have these classes without any relationships because they are not directly linked?
Any Idea

Hi Tonny,
Interesting question. It depends on the underlying paradigm behind your architecture/design. When you apply the true OO paradigm, you begin with objects. A class is nothing more than a way of categorizing objects with similar behaviour and/or attributes. Objects don't sit in isolation in a given system. They collaborate/interact with one another to realize various System functionality. When you classify the objects into classes, you will have associations between them that show how they relate to each other.
In your example, it looks like you have simply taken a relational model and have used OO notations to denote the relational entities. You could call it a "class model" but it is still a relational model represented using OO notations. It is not the notation but the driving paradigm that qualifies something an Object Oriented design.
Besides, what would be the purpose of such a class diagram? OO approach is not the solution for all kinds of Systems or domains. In some cases, as in this example, you are better served by a traditional notation such as E-R notation.

Regards
Sridhar

Thanks for your reply Sridhar, I appreciate it

Originally posted by Sridhar Raman:

Objects don't sit in isolation in a given system. They collaborate/interact with one another to realize various System functionality. When you classify the objects into classes, you will have associations between them that show how they relate to each other.

Well, that is true, but in my case, the Session Facade will be the controller that actually links these "domain objects" together.
They are actually desperate systems sitting in different places, and accessed using Corba/Web services. The application has combine the use of all these systems to make something useful out of it. So I represent the �data� accessed by each system as a �Domain Class�, and have a DAO for each to access the system, and when running a Session Bean will be accessing these �Domain Classes� and follow the use case flow to make use of these systems. The problem is that I think Design before Thinking Analysis, and the controller (Session Bean) and DAO�s are all design classes. I want to draw a class diagram to show how my classes relate to each other and later draw a sequence diagram showing the flow of message passing between running objects.
Any ideas? Go GO Architectsm !