Sequence Diagram
Complements a use case with details of workflow events.
A sequence diagram is an interaction diagram that highlights the order in which instructions are executed/messages are exchanged
- Component symbols: lifeline/activation box/option loop/alternative
- Message symbols (arrows): synch/asynchronous message
Instances of the actors are placed at the top of the diagram.
Lifelines represent either roles or object instances that participate in the sequence being modeled.
Activation boxes represent the time needed for an object to complete a task. The longer a task takes, the longer the activation box.
To show interaction, an arrow is drawn from the sending object to the receiving object. A solid arrowheard for sync operations, A stick arrowhead for async operations.
On the same lifeline, a higher message precedes a lower message and Message sending precedes message receiving.
An alternative can be used to show multiple/branching cases
A loop can be used to show repeating things
A timeout can indicate an action that only repeats after a certain interval has passed
A parallel can be used to indicate two things that happen simultaneously
