Read First: Event Diagram, Event, Event Type A creation event of an event diagram means "the event diagram has started". It is called "creation" because an instance of the operation is created to model the running process. Creation event types are notated in OOIE with a bulls-eye preceding it. Once an event diagrams is started, it may take an arbitrarily long time to finish. For example:In the above case, the event Bill Paid may a take a long time to happen, or may not happen at all. When the event diagram execution waits at the control condition, it is still running, but it is waiting. Events that are not creation events, like Bill Paid, are called external events, meaning they are caused by operations that are not controlled by the diagram (see Operation^IsExternal). Diagrams that do no preparation before waiting for an event to happen can omit the creation event: The above event diagram has no creation event, since there is no preparation to answering the phone, but someone must still start executing the diagram at the beginning of business to detect the Phone Rang event. The diagram has a trigger rule to terminate itself at the end of the day. Omitting the creation event is purely a presentation shorthand, so the model underlying the diagram should still have a creation event even though it isn't displayed. The model for the above diagram would actually look like this: The creation event does not trigger anything, because its only function is make the diagram active, so it waits for the phone to ring. Getting information into an event diagram The creation event does not contain any information about what started the event diagram, only that it has started with certain values of its input variables. In contrast, a external event is waiting for a particular object to change state, so the event diagram is tied to what will cause it to start processing. In both cases, the event diagram has access to information passed in through its input variables. In the external event case, additional information is available in the event object. For example, if a external event type is Traffic Light Changed Color, the event object will contain the specific traffic light and specific color. Read First: Event Diagram, Event, Event Type