What comes first: the activity diagram or the sequence diagram?

Question

I've been learning about UML diagrams and such. While doing so I came across a problem. Which diagram should be drawn first when designing a system, given that use case and such are completed? Is the activity diagram drawn before or after the sequence diagram?

Answer 1

There is no order for the creation of diagrams, of any type. Depending on your project, you may not even find use for some diagram types. That said, I would expect that activity diagrams, if created, would be created earlier than sequence diagrams. Activity diagrams represent workflows and processes and show sequence and concurrency of steps, and do so without showing design details of modules, classes, and methods. Sequence diagrams typically show the interaction between classes, instances of those classes, and the method calls (with arguments). The information shown in an activity diagram is known earlier in a project and is independent of things like technology choice, which may change how you consider the items shown in a sequence diagram.

Answer 2

There is no privileged order, but I like to draw the activity diagram first. Activity diagrams make me know and understand all the possible successful scenarios (happy paths) as well as the unsuccessful ones.