Especially, it can be used for describing concurrent interrelated activities. However, Petri nets may be outside the desired scope of the course. Sequence diagrams may not be suitable for parallel system description. Scenarios may have too many cases to be suitable. So let us focus on activity diagrams.
Activity diagrams .
An activity diagrams is a state machine-like construct focusing on activities, which are states in which some computational activity is taking place. Activity diagrams show these activities, relationships among them, and the possible state transitions depending on different conditions. Heavy bars with more than one incoming or outgoing arrow indicate the start or end of concurrent processing. Activity diagrams are used to model sequences of actions and conditions within a process. They are like flow charts in important ways, but differ in supporting parallel activities and their synchronization.