Moving Towards Specifications
\n\u2022 What functions will the new system provide?
\n\u2013 How will people interact with it?
\n\u2013 Describe functions from a user\u2019s perspective
\n\u2022 UML Use Cases
\n\u2013 Used to show:
\n\u2022 the functions to be provided by the system
\n\u2022 which actors will use which functions<\/p>\n
Capture the relationships between actors and use cases.<\/p>\n
A\u00a0use case diagram<\/b>\u00a0is a graphical depiction of a user’s possible interactions with a system. A use case diagram shows various use cases and different types of users the system has and will often be accompanied by other types of diagrams as well. The use cases are represented by either circles or ellipses. The actors are often shown as stick figures.<\/p>\n While a\u00a0use case<\/a>\u00a0itself might drill into a lot of detail about every possibility, a use-case diagram can help provide a higher-level view of the system. It has been said before that “Use case diagrams are the blueprints for your system”.[1]<\/a><\/sup><\/p>\n Due to their simplistic nature, use case diagrams can be a good communication tool for\u00a0stakeholders<\/a>. The drawings attempt to mimic the real world and provide a view for the\u00a0stakeholder<\/a>\u00a0to understand how the system is going to be designed. Siau and Lee conducted research to determine if there was a valid situation for use case diagrams at all or if they were unnecessary. What was found was that the use case diagrams conveyed the intent of the system in a more simplified manner to\u00a0stakeholders<\/a>\u00a0and that they were “interpreted more completely than class diagrams”.<\/p>\n \u2022 Look for: Finding Use Cases 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. <\/sup>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","protected":false},"excerpt":{"rendered":"Application<\/span><\/h4>\n
Identifying Actors<\/h4>\n
\n\u2013 the users who directly use the system
\n\u2013 also others who need services from the system
\n\u2022 To find actors that are people\/roles ask:
\n\u2013 Who will be a primary user of the system? (primary actor)
\n\u2013 Who will need support from the system to do her daily tasks?
\n\u2013 Who will maintain, administrate, keep the system working?
\n(secondary actor)
\n\u2013 Who or what has an interest in the results that the system produces ?
\n\u2022 To find actors that are external systems ask:
\n\u2013 Which hardware devices does the system need?
\n\u2013 With which other systems does the system need to interact with?<\/p>\n
\n\u2022 For each actor, ask the following questions:
\n\u2013 Which functions does the actor require from the system?
\n\u2013 What does the actor need to do?
\n\u2013 Does the actor need to read, create, destroy, modify, or store some kinds of information in the system?
\n\u2013 Does the actor have to be notified about events in the system?
\n\u2013 Does the actor need to notify the system about something?
\n\u2013 What do those events require in terms of system functionality?
\n\u2013 Could the actor\u2019s daily work be simplified or made more efficient through new functions provided by the system?<\/p>\nUML Sequence Diagrams<\/h3>\n