\u2022 Sequence Diagrams are interaction diagrams that detail how operations are carried out<\/p>\n
\u2022 Interaction diagrams model important runtime interactions between the parts that make up the system<\/p>\n
\u2022 Interactions Diagrams<\/p>\n
\u2022 capture the interaction between objects in the context of a collaboration<\/p>\n
\u2022 show object instances that play the roles defined in a collaboration<\/p>\n
\u2022 show the order of the interaction visually by using the vertical axis of the diagram to represent time what messages are sent and when<\/p>\n
\u2022 show elements as they interact over time, showing interactions or interaction instances<\/p>\n
\u2022 do not show the structural relationships between objects<\/p>\n
A\u00a0sequence diagram<\/b>\u00a0or\u00a0system sequence diagram<\/b>\u00a0(SSD) shows\u00a0process<\/a>\u00a0interactions arranged in time sequence in the field of\u00a0software engineering<\/a>. It depicts the processes involved and the sequence of messages exchanged between the processes needed to carry out the functionality. Sequence diagrams are typically associated with use case realizations in the\u00a04+1 architectural view model<\/a>\u00a0of the system under development. Sequence diagrams are sometimes called\u00a0event diagrams<\/b>\u00a0or\u00a0event scenarios<\/b>.<\/p>\n For a particular scenario of a\u00a0use case<\/a>, the diagrams show the events that external actors generate, their order, and possible inter-system events. All\u00a0systems<\/a>\u00a0are treated as a\u00a0black box<\/a>; the diagram places emphasis on events that cross the system boundary from actors to systems. A system sequence diagram should be done for the main success scenario of the\u00a0use case<\/a>, and frequent or complex alternative scenarios.<\/p>\n A sequence diagram shows, as parallel vertical lines (lifelines<\/i>), different processes or objects that live simultaneously, and, as horizontal arrows, the messages exchanged between them, in the order in which they occur. This allows the specification of simple runtime scenarios in a graphical manner.<\/p>\n A system sequence diagram should specify and show the following:<\/p>\n Professionals, in developing a project, often use system sequence diagrams to illustrate how certain tasks are done between users and the system. These tasks may include repetitive, simple, or complex tasks. The purpose is to illustrate the\u00a0use case<\/a>\u00a0in a visual format. In order to construct a system sequence diagram, you need to be familiar with the\u00a0unified modeling language<\/a>\u00a0(UML). These models show the logic behind the actors (people who affect the system) and the system in performing the task. 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). Under each actor or system there are long dotted lines called lifelines, which are attached to them. Actions are performed with lines that extend between these lifelines. When an action line is connected to a lifeline it shows the interaction between the actor or system. Messages will often appear at the top or bottom of a system sequence diagram to illustrate the action in detail. For example, the actor could request to log in, this would be represented by login (username, password). After each action is performed, the response or next action is located under the previous one. As you read down the lines you will see in detail how certain actions are performed in the provided model, and in what order.<\/p>\n","protected":false},"excerpt":{"rendered":"Key elements<\/span><\/h4>\n
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Reading a system sequence diagram<\/span><\/h4>\n