CS 501: Software EngineeringAdministrationDiagrams and Specification in UMLActor and Use Case DiagramUse Cases and ActorsScenarioScenario: a Typical StudentScenario (continued)Slide 9Modeling Scenarios as User CasesUse Cases for Quiz SystemSlide 12Relationships Between Use Cases: <<includes>>Relationships Between Use Cases: <<extends>>Use Cases in the Development CycleDocumentationRequirements Specification: PurposeSlide 18Slide 19Details in RequirementsDocumentation of Use CaseSpecification of Use Case (continued)Requirements Specification: ProcessRequirements Analysis v. System Design1CS 501 Spring 2005CS 501: Software EngineeringLecture 8Requirements II2CS 501 Spring 2005AdministrationQuiz 1Collect after class or from reception at 301 College AvenueAssignment 1: Feasibility studyDue Friday at 5:00 p.m.Remember to submit your questionnairesRemember to send a copy to your client3CS 501 Spring 2005Diagrams and Specification in UMLA diagram is the graphical representation of a set of elements, usually rendered as a connected graph of vertices (things) and arcs (relationships).Each diagram is supported by technical documentation that specifies in more detail the model represented by the diagram.A diagram without documentation is of little value.4CS 501 Spring 2005Actor and Use Case Diagram• An actor is a user of a system in a particular role. An actor can be human or an external system.• A use case is a a task that an actor needs to perform with the help of the system.Borrow bookBookBorrowerUse cases make more precise the concept of viewpoint analysis.5CS 501 Spring 2005Use Cases and Actors• A scenario is an instance of a use case • Actor is role, not an individual(e.g., librarian can have many roles)• Actor must be a "beneficiary" of the use case(e.g., not librarian who processes book when borrowed)In UML, the system boundary is the set of use cases.6CS 501 Spring 2005ScenarioA scenario is a tool used during requirements analysis to walk through a specific interaction with a proposed system.ExampleThe requirements are being developed for a system that will enable university students to take quizzes online from their own rooms using a Web browser.Create a scenario for a typical student.7CS 501 Spring 2005Scenario: a Typical StudentIndividual: Philip Glass, senior at Cornell, major in computer science, location Risley Hall.Equipment: Dell laptop attached to Cornell dormitory network. Mozilla 5.1 browser and Sidecar authentication system installed.Scenario: 1. PG powers up computer and authenticates using Sidecar.2. PG starts browser and types URL of Quiz system.3. Quiz system displays list of options.8CS 501 Spring 2005Scenario (continued)4. PG selects CS 501 Quiz 1.5. A list of questions is displayed, each marked to indicate whether completed or not.6. PG selects a question and specifies whether he will submit a new answer or edit a previous answer.7. For the first question, he is submitting a new answer. He has a choice whether to type the solution into the browser or to attach a separate file. He decides to attach a file.8. For the second question, he is editing a previous answer. He chooses to delete a solution previously typed into the browser, and to replace it with an attached file.9CS 501 Spring 2005Scenario (continued)9. PG has now completed the quiz. He selects an option that submits the quiz to the grading system.10. PG now wishes to change a solution. The system does not permit changes once the solution has been submitted.11. PG logs off.10CS 501 Spring 2005Modeling Scenarios as User CasesA scenario is useful in discussing a proposed system with a client, but needs to be generalized as part of the requirements modeling.A use case provides such a model.11CS 501 Spring 2005Use Cases for Quiz SystemTakeQuizQuizTakerCheckGradesRequestRegrade12CS 501 Spring 2005Use Cases for Quiz SystemSetQuizInstructorGradeRegradeNote that actor is a role. An individual can be a QuizTaker on one occasion and an Instructor at a different time.13CS 501 Spring 2005Relationships Between Use Cases: <<includes>>QuizTakerAuthenticateTakeQuiz<<includes>><<includes>>CheckGrades14CS 501 Spring 2005Relationships Between Use Cases: <<extends>>TakeQuizQuizTakerConnectionFails<<extends>><<include>> is used for events that are in the flow of events of the source use case.<<extends>> is used for exceptional conditions, especially those that can occur at any time.15CS 501 Spring 2005Use Cases in the Development Cycle• Use cases are a tool in requirements analysis• Intuitive -- easy to discuss with clients• Use cases are often hard to translate into class models• Scenarios are useful to validate use cases and the design of a system.16CS 501 Spring 2005DocumentationReasons for documentation:visibility (e.g., project plan, interim report) user support (e.g., user manual) team communication (e.g., interface specifications)maintenance and evolution (e.g., requirements) Characteristics of documentation:accurate and kept currentappropriate for audiencemaintained online (usually)simple but professional in style and appearanceDocumentation is expensive --> Quality not volume17CS 501 Spring 2005Requirements Specification: Purpose1. Document that describes the requirements to the stakeholders in a precise manner• Expressed in the terms that the stakeholders understand• As precise and specific as possible• Comprehensible from many viewpoints• Reviewed by stakeholders so that they understand implications• Must be clear about assumptions (things left out)18CS 501 Spring 2005Requirements Specification: Purpose2. It describes the requirements to the implementers• As precise and specific as possible• Expressed in terms that they understand• Comprehensible to new team members19CS 501 Spring 2005Requirements Specification: Purpose3. It records the requirements for the future• An essential part of system evolution4. It may be a contractual document20CS 501 Spring 2005Details in RequirementsRequirements must be specificExamples -- university admissions system Requests for information received by email must be answered within one business day.An admissions officer who is talking to an applicant by telephone must be able to retrieve the applicant's records within 10 seconds.No financial aid offer may exceed the maximum defined in Section 8.7.21CS 501 Spring 2005Documentation of Use
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