Sun Education creating its own standard: there is nothing in UML standards that mention that class diagrams cannot be broken down into manageable parts; rather, that is the standard with the industry.
If they don't want that then they should explicitly mention that. In fact, in my assumptions I had mentioned that I am doing this for less prolixity and better clarity. Still, it has been ignored.
There is a self-proclaimed Sun evaluator who wrote a book where he mentioned 'do this' or 'do that' that I saw recently. If such person can prescribe or proscribe, why not Sun? By not doing so, the test-takers would be indirectly invited to follow non-standard practices.
Again, the number of details (read the number of classes) may vary. In such case, it is preposterous to presume that there will be no need to break down the assignment into multiple class diagrams, as mentioned by the same Sun evaluator.
By following the same principles of abstractions, the only logical approach to alternative way to specialize class diagrams would be to use meta model or meta object facility, which are rather new developments and by not specifying version of UML to be used, Sun Education seems to preempt such possibility.
I think that it's more simpler that you think. The purpose of doing an assignment is to solve a business problem, and for us, as test takers the target is that assessor agrees that a proposed solution is efficient, consistent and solves this problem. If class diagram is split into multiple parts is is harder to understand (yes, possible, but not clear) the overall architecture.
The message from an assessor is that the level of the detail should be such that there is no need to split diagram. Sure you can put additional details there, but this won't help to solve the problem, if the overall structure is clear and right then assessor will no need additional details, you can just write that "this is done according this pattern, enterprise beans implement required interfaces" and so on.
I split my class diagrams up. There was no way I could fit all my classes on a single, manageable, diagram. However, the split was along consistent and clearly defined lines.Each diagram had a clearly defined singular purpose. To avoid any ambiguity, I also used my supporting documentation to spell out my reasons for doing so.