Review Sequence diagram notation


	Lesson 2 Objective	Review: sequence diagram notation Review the notation for a sequence diagram.
		Sequence diagram notation The sequence diagram illustrates objects talking to one another over time. To do so, the diagram uses objects, timelines, and event arrows. The diagram consists of a set of participating objects lined up across the top of the diagram. A timeline is drawn down from each object. Sequence Diagram Example You will note from the diagram above: The objects use standard object notation, that is, a rectangle containing the object name, a colon, and the class name of the object. All three of these elements are underlined. The object name is optional. You may use just the colon and class name: ObjectName:ClassName The timeline is a vertical dashed line. The events appear as arrows. Event Shown Horizontal An event is shown as a horizontal arrow from the timeline of the "sending" object to the timeline of the "receiving" object. A return from an event is shown as a horizontal arrow from the "receiving" object back to the "sending" object. Return Arrow Line Some tools support a different kind of line for the return arrow, for example, a dashed line instead of a solid line. This is extremely useful because the two events are handled so differently. The order of events The position on the timeline indicates a relative point in time. The top of the line represents the beginning of the timeline. The bottom represents the end of the timeline.