Usecase diagrams with extends dependency

Question

Hi,
I've a doubt regarding the use of <<extends>> in usecase.
Suppose we are creating usecase diagram for a screen for entering personal details(usecase name - Set Up Person). That screen contains a button for another window , let it be company details for the person(usecase name - Set Up Company). In detailed usecase I've decided to go to create usecase diagram for both company snd person. Can I draw the 'Set Up Person' usecase diagram for extending 'Set Up Company' usecase. It means that the user may invoke and enter the "company details" for the person.
It's not a mandatory option.
Does it make sense?Pls guide me on right way....Also Pls give more input regarding <<include>> and <<extend>>
(Set Up Person) -----<<extends>>-----> (Set Up Company)

Answer 1

In some cases we can exccute a use case from another one optionally.
In this case we can go for <<extend>> relationship.I disagree. I don't think it is to do with whether a use case playing a part in another is mandatory or optional. Either way, the use case that plays such a part as a self contained chunk of functionality would be <<include>>
So your SystemLogin example is correct in this manner.
I think extend is where a use case does the same thing as another in more detail adding something more and thus providing additional benefit to the user.
The example I have at hand from "Using UML" Stevens & Pooley (Addison Wesley) shows a simulation system where:
     O
    /|\ ------ <observe behaviour> --- <<include>> ---> <run model>
    / \                ^
EXPERIMENTOR          /|\
                       | <<extend>>
                 |
              <collect statistics>