Use Case diagram

[rezaTech]

hello there
In the use case diagram, is it necessary to maintain activity sequence? meaning, i have 4 use cases (uc1, uc2, uc3, uc4), in terms of activity actor does that in sequence. But when i draw the use case diagram, if I draw them randomly i.e. uc1, uc3, uc4, uc2, is it allowed? or it is necessary to draw sequentially.

My second question is, actor can not do uc2 without doing uc1. If I draw uc1 and uc2 and make an association relation with the actor, is it alright?
or I have to draw uc1, connect it with the actor and then draw uc2 and connect it with uc1?
which one is correct?

is there any help?

[jeshaw2]

The answer to #1 is that they don't have to be drawn sequentially.
The answer to #2 is that the Precondition for uc2 is the successful completion of uc1.

A larger concern is that the need to ask these questions indicates that your use cases are at too low of a level, not high level, business use cases.  You might ask yourself "what is the  single business goal that is attained by the completion of your use case sequence?"

[«Midnight»]

To elaborate on parts of what Jim says...

More specifically, use cases do not have the semantic rigor to specify or support activity (or other) sequence. You are welcome to draw a use case diagram in any fashion or with any convention you choose, which might imply a given order. However, this should only be taken as inferring the order. Perhaps you have used a tool that makes use of this, but that would be a custom extension to UML. A UML use case model will neither define nor enforce any ordering.

As to Jim's ending comment, I fully agree. Consider some other model form.

[As an exercise, consider a use case that encompasses the ones you currently have - where your current use cases might all be found by drilling into the higher level case. Try elaborating this higher level use case with some additional detail, in the form of one or more activity diagrams, state models, and sequence diagrams. You can easily do this in EA by right-clicking use case and choosing Add from the context menu. Once you've finished elaborating the higher-level use case, do you still find the lower-level ones to be necessary? If so, can you now simplify their interrelationships? Has the need to imply order in the use case model been satisfied?

HTH, David

David

[rezaTech]

Thank you both for answering.

[«Midnight»]

But did it help you to move your project forward?

[rezaTech]

hi
hmmm yes it did.
Actually i had an argue with my friend about that matters before starting a new project.