CS 501: Software EngineeringCourse AdministrationDiscussion of Feasibility StudyQuiz 1 (c)Slide 5Slide 6Slide 7Software Development Principles and PracticesModeling Techniques for Requirements Analysis and DefinitionDecision Table: Bad ExampleDecision Table: Good ExampleData-Flow ModelsData-Flow Example: University AdmissionsData-Flow Example: Assemble Application StageData-Flow Example: Process Completed Application StageProcedural Models: FlowchartFlowchart: University AdmissionsProcedural Models: Pseudo-codeEntity-Relation ModelEntity-Relation DiagramExample: CS 501 ProjectExample: Schema for Web DataMARC Format for BooksPart of an Entity-Relation Diagram for MARCData DictionariesPetri NetsTransition DiagramsTherapy Control Consol: ScenarioTherapy Control Consol: Finite State MachineState Transition DiagramTherapy Control Consol: State Transition TablePrototyping RequirementsA Note on Object Models1CS 501 Spring 2005CS 501: Software EngineeringLecture 9Requirements 32CS 501 Spring 2005Course AdministrationFeasibility StudyEverybody should received comments shortly.Teaching Assistants have been assigned.Quiz 1Uncollected answer books are at the reception at 301 College Avenue.3CS 501 Spring 2005Discussion of Feasibility StudyGeneralWho will read the feasibility study?What is needed to decide to go ahead?Scope and understanding of projectStatement of the task Preliminary requirements and technical analysisDeliverables and business considerations ConfidenceOutline plan. Does it inspire confidence?Visibility plan. How will progress be reported? Risk analysis. How are the risks to be minimized?4CS 501 Spring 2005Quiz 1 (c)A U.S. government agency, which manages huge numbers of documents, has received funds to build a large-scale computer system. The agency proposes to use a waterfall model of software development, but an independent study recommends a phased development using iterative refinement in the first phase and a waterfall model in the second.[On the next three slides, a short answer is given in Roman type. Material in italic extends the short answers.]5CS 501 Spring 2005Quiz 1 (c)i Before this system is implemented some difficult technical choices have to be made. How much should the choice of technology be considered during the feasibility study?During the feasibility study, it is necessary to know that there is at least one technical approach that would allow the system to be built. It should be studied in sufficient detail to allow estimates of costs and time table.If there appear to be several very different technical approaches possible, more than one might be analyzed in sufficient detail to understand the implications for the costs and timetable.In this project, the feasibility study should also plan the process by which the technical decisions will be made.6CS 501 Spring 2005Quiz 1 (c)ii These technical choices are one of the reasons that iterative refinement is recommended for the first phase of development. Why? The first iteration will use the team's initial technical knowledge, but will likely show weaknesses in the approach chosen. Subsequent iterations will replace or improve aspects of the technical choices until a version is established that meets the requirements of the project.A waterfall model is unsuitable because of the large-scale changes that may need to be made. Because of uncertainty, it is difficulty to judge the cost and timetable of the project until this stage is complete.7CS 501 Spring 2005Quiz 1 (c)iii What is the advantage of using the waterfall model in the second phase?The waterfall model with feedback is an effective way to build a system that is well understood, so that few changes are likely to be made in either the requirements or the design. At its best, a waterfall process results in each stage being done once and being done well. For this system, the iterations made during the first phase should have created a high level of understanding and agreement about the entire system.8CS 501 Spring 2005Software Development Principles and PracticesSoftware developmentSoftware development is a craft. Software developers have a variety of tools that can be applied in different situations. Part of the art of software development is to select the appropriate tool for a given implementation9CS 501 Spring 2005Modeling Techniques for Requirements Analysis and DefinitionThe craft of requirements analysis and specification is to select the appropriate tool for the particular task.• A variety of tools and techniques. • Many are familiar from other courses.• There is no correct technique that fits all situations.As you build understanding of the requirements through scenarios and use cases, use modeling tools to specify requirements. The models provide a bridge between the client's understanding and the developers.10CS 501 Spring 2005Decision Table: Bad ExampleUniversity Admission DecisionNote that the rules are too vague.High SAT T F F F F FHigh grades - T F F F FSports - - T T F FRecommendations - - T F T FReject X X XAccept X X X11CS 501 Spring 2005Decision Table: Good ExampleUniversity Admission DecisionNote that the rules are now specific and testable.SAT > S T F F F F FGPA > G - T F F F FAthletics code = - - T T F FRecommendations > A- - - T F T FSend rejection letter X X XSend acceptance letter X X X12CS 501 Spring 2005Data-Flow ModelsExternal entitiesProcessing stepsData stores or sourcesData flowsAn informal modeling technique to show the flow of data through a system.13CS 501 Spring 2005Data-Flow Example: University AdmissionsApplicantApplicationformReceiveapplicationCompletedapplicationEvaluateRejectionAcceptanceShows the flow, but where is the data stored?14CS 501 Spring 2005Data-Flow Example: Assemble Application StageApplicantApplicationformReceiveCompletedapplicationSupportinginformationPendingdatabaseAcknowledgmentInitiateevaluationApplicantdatabaseEvaluationrequestANDANDAcknowledgmentDoes this model cover all applications? Are there special cases?15CS 501 Spring 2005Data-Flow Example:Process Completed Application StageRejectionEvaluationApplicantdatabaseEvaluationrequestAcceptanceFinancial aidOfferSpecialrequestThe data-flow diagram will need specification of the decision-making process.16CS 501 Spring 2005Procedural Models: FlowchartOperationDecisionManual operationReportAn informal modeling technique to show the decisions and paths that data takes through a system.17CS 501 Spring 2005Flowchart:
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