UML related questions

[Sayan Mukherjee]

Hi,

In UML there are a set of diagrams each of which gives
a different view of the system (to be built). These diagrams
are supposed to help in development and testing of this system.

My question is: Of these diagrams which are the mandatory
ones for the development of a system, if not all?

What I mean is, is there any diagram in the UML repository
whose utility in design and construction benefit may otherwise
be obtained from the other diagrams as well?

Example 1 (new system being created):
The coding for a system is supposed to start after the class
diagrams are ready. What are the UML diagrams mandatorily
required to be created so that one can reach the creation stage
of class diagrams in the most efficient way?

Example 2 (existing system being rewritten on a new
technology platform):
There is a system already implemented and there is a change
in the technology platform. Assume that apart from functionality
documents and the working system, there is no other resource
available. In this case, what are the UML diagrams that need to
be created mandatorily so that the class diagrams can be
arrived at for the development of the same system on the new
technology?

Any answer, generic or specific to the above examples,
will be appreciated.

Thanks in advance.

[vcstarter]

In UML, it is good to sart with a Use Case Diagram. The use case diagram can be considered as the engry point of the system. This diagram show the outside view of the system. A use case diagram does not have to be technical. Anybody who does not know anything about the system should understand the use case diagram. So, you can consider the use case diagram is important.

If you design a system from scratch, you will need to derrive you class somewhere. Sometime, for complex system it is very difficult to figure out classes. This is whe other dagram makes sense. For example, from the use case diagram you have defined both your use cases an actors. You analyze each use case related to your rquirement. From this information, you can get collaboration diagram, sequence dagram, and activity diagram. The class diagram will be your last ressort.

Let me know if the info is helpful.

[Sayan Mukherjee]

Hello vcstarter,

That was a great help and thanks for the encouraging note of
your reply. I fully agree with you on the importance of the
Use Case diagrams as a starting block.

Thanks again.