I'm trying to draw a UML activity diagram for the functionality of a user retrieving his password when she has forgotten it. It looks like this:
As you can see, this functionality requires two requests at different stages, one for the input of the username, the other for the input of the verification code. So the whole procedure could be divided into two sub-procedures each representing a single request and response pair. That's why I wonder whether I should use one or two activity diagrams to illustrate this functionality. Should an activity diagram correspond to a single functionality or to a single request/response pair?
In my opinion, the former one brings completeness, but increases complexity. The complexity could be solved by the latter one, but it also brings partition and dependency issues. It's hard to decide for me, please give me some suggestions.