Messages will often appear at the top or bottom of a system sequence diagram to illustrate the action in detail. When an action line is connected to a lifeline it shows the interaction between the actor or system. Actions are performed with lines that extend between these lifelines. Under each actor or system there are long dotted lines called lifelines, which are attached to them. Reading a sequence diagram begins at the top with the actor(s) or the system(s) (which is located at the top of the page). These models show the logic behind the actors (people who affect the system) and the system in performing the task. In order to construct a system sequence diagram, you need to be familiar with the unified modeling language (UML). The purpose is to illustrate the use case in a visual format. These tasks may include repetitive, simple, or complex tasks. Professionals, in developing a project, often use system sequence diagrams to illustrate how certain tasks are done between users and the system. Indication of any loops or iteration area.Return values (if any) associated with previous messages.Messages (methods) invoked by these actors.This allows the specification of simple runtime scenarios in a graphical manner.Ī system sequence diagram should specify and show the following: Key elements of sequence diagram Ī sequence diagram shows, as parallel vertical lines ( lifelines), different processes or objects that live simultaneously, and, as horizontal arrows, the messages exchanged between them, in the order in which they occur.
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