I am drawing uml diagrams for bank mgmt systems. I made use case diagram in VP suite. http://imgur.com/8Toku.png . I dont know how to proceed with conceptual class and sequence diagram. Help needed?
First of all, I question the usefulness of the use case diagram you presented. Use cases are meant to illustrate what user goals are to be satisfied by the system being modelled. Use cases such as Login and Logout may contribute to an overall goal but by themselves, they are meaningless goals. It’s like saying, “I’m going to use this system to login.” From the user’s point of view, what goal is that accomplishing?
One may argue that Login is an extension of the Online Transaction use case. What goal does “online transaction” accomplish? What is the user trying to do here? Would a user say, “I’m going to use this system to perform an online transaction?” What exactly is the user accomplishing here?
Some examples that pop into my head for a banking system would be Withdraw Cash and Deposit Cash use cases. Certainly users would say, “I’m going to use this system to withdraw cash” and “I’m going to use this system to deposit cash”.
Borrowing the rules of thumb mentioned in Craig Larman’s Applying UML and Patterns, there are three tests to consider when determining whether a use case is useful:
In the boss test, you pretend that your boss is asking you, “what have you been doing today at work?” If you answer something like, “logging into the system,” would your boss be happy?
In the EBP test, you consider whether the use case is performed by a single person at a time that adds value to a business. For example, “approving credit.”
In the size test, you consider how many steps are needed to accomplish the use case. Use cases typically have many steps. In the book, Larman presented the following examples:
Negotiating a supplier contract is too broad, handling returns is okay with the boss and seems like an EBP so this is good. Logging in is something the boss wouldn’t be happy with. Finally, Moving a game piece is a single step, which fails the size test.
Now, to answer your original question…
To proceed from a use case to a domain/conceptual class diagram, you need to consider all the elements in play in the use case description. Those may be potential class entities. A common trick is to highlight all the nouns in your use case descriptions and consider them to be potential entities to be relevant in your class diagram.
To process from a use case to a domain/conceptual sequence diagram is a bit simpler. Essentially, you are writing your use case description into UML form. The class diagram you came up with may help you in deciding which lifelines are relevant for depicting the sequence.
Hope that helps. I recommend Craig Larman’s Applying UML and Patterns – I think it’s a good and insightful read.
