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with a circle and denotes something that happens (compared with an activity, which is something that is done). Icons within the circle denote the type of event (e.g., an envelope representing a message, or a clock representing time). Events are also classified as catching (for example, if catching an incoming message starts a process) or throwing (such as throwing a completion message when a process ends).
:; Start event
:: Acts as a process trigger; indicated by a single narrow border, and can only be catch, so is shown

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