Showing the flow of control in interactions by using execution
occurrences
In sequence diagrams, execution occurrences represent
the behavior of a participant on a lifeline that is bound by a start event
and a finish event. You can add, resize, move, and delete execution
occurrences in an interaction.
Creating execution occurrences
In sequence diagrams, an execution occurrence is created automatically when you create a synchronous or an asynchronous message. You can create an execution occurrence manually to show the start and finish behavior in an interaction. You can also nest execution occurrences to indicate nested behavior in a call sequence.
Resizing and reordering execution occurrences
In sequence diagrams, an execution occurrence automatically resizes vertically to indicate the time during which a participant is active. The top of the execution occurrence aligns at the point where the message is received and initiates the behavior; the bottom aligns with the finish of the behavior during an interaction. If you resize the execution occurrence across any messages and fragments, the execution occurrence reorders in the interaction.