Use Cases and Scenarios<\/p>\n
\u2022 A use case is a collection of interactions between external actors and a system
\n\u2022 In UML, a use case is \u201cthe specification of a sequence of actions, including variants, that a system (or entity) can perform, interacting with actors of the system.\u201d
\n\u2022 Typically each use case includes a primary scenario ( or main course of events) and zero or more secondary scenarios that are alternative courses of events to the primary scenario.
\n\u2022 In RUP (Rational Unified Process), user requirements are captured as use cases that are refined into scenarios.
\n\u2022 Then: A scenario is one path or flows through a use case that describes a sequence of events that occurs during one particular execution of a system.<\/p>\n
Sequence Diagram Tutorial<\/p>\n
A sequence diagram or system sequence diagram (SSD) shows process interactions arranged in time sequence in the field of software engineering. 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 4+1 architectural view model of the system under development. Sequence diagrams are sometimes called event diagrams or event scenarios.<\/p>\n
For a particular scenario of a use case, the diagrams show the events that external actors generate, their order, and possible inter-system events.[1] All systems are treated as a black box; 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 use case, and frequent or complex alternative scenarios.<\/p>\n
A 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. 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 use case in a visual format. In order to construct a system sequence diagram, you need to be familiar with the unified modeling language (UML). These models show the logic behind the actors (people who affect the system) and the system is 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":"