UML - Sequence Diagram how to show alternate course

问题

I've a function called logon(uname,pass) which returns either success or failure message. Should i show this as ALT fragment?

Basically I'm after transforming this use case to sequence diagram:

> main flow:
> 1. User provide username password.
> 2. Display successful message after logon.
> 
> alternate flow:
> 1. User provide invalid username and passsword.
> 2. Display invalid username or passwrod message.

Thanks

回答1:

See this example.

Having said that, I'm with @Tanparmaiel in preferring an activity diagram for alternatives: much more visually intuitive.

hth.

回答2:

You should use an Activity diagram which depicts the workflow of the action/activities of your application. The sequence diagram shows how the processes interact with one another and in what order.

来源：https://stackoverflow.com/questions/6000268/uml-sequence-diagram-how-to-show-alternate-course