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ODU CS 350 - Lecture Notes

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CS 350: Introduction to Software EngineeringLecture TopicsWhat is Quality?The PSP Quality Focus -1The PSP Quality Focus -2The Economics of QualityTesting Alone is IneffectiveRemoving Defects in TestQuality and ProductivityDefect-removal Methods -1Defect-removal TimesDefect-removal Methods -2Defect-removal Rates -1Slide 14Why Reviews are EfficientReview PrinciplesThe Code Review ChecklistDesign Review PrinciplesReviewable DesignsThe Design Review StrategyQuality MeasuresPhase YieldYield EstimatesPotential Control ParametersSlide 25Yield versus Review Rate -3Defect Removal Leverage (DRL)Cost of Quality (COQ) -1Cost of Quality (COQ) -2Cost of Quality (COQ) -3Review ConsiderationsReviewing Before CompileSlide 33Slide 34Reviews and InspectionsDefect PreventionDefect Prevention Strategy -1Defect Prevention Strategy -2Messages to RememberCS 350: Introduction toSoftware EngineeringSlide Set 5Software QualityC. M. OverstreetOld Dominion UniversityFall 2005Fall 2005 CS 350/ODULecture Topics What is quality?The economics of qualityDefect-removal methodsDesign and code reviewsQuality measuresReview considerationsFall 2005 CS 350/ODUWhat is Quality? Basic definition: meeting the users’ needsneeds, not wantstrue functional needs are often unknowableThere is a hierarchy of needs.Do the required tasks.Meet performance requirements.Be usable and convenient.Be economical and timely.Be dependable and reliable.Fall 2005 CS 350/ODUThe PSP Quality Focus -1To be useful, software must install quickly and easilyrun consistentlyproperly handle normal and abnormal casesnot do destructive or unexpected thingsbe essentially bug-freeDefects are not important to users, as long as they do notaffect operationscause inconveniencecost time or moneycause loss of confidence in the program’s resultsFall 2005 CS 350/ODUThe PSP Quality Focus -2The defect content of software products must be managed before more important quality issues can be addressed.Low defect content is an essential prerequisite to a quality software process.Since low defect content can best be achieved where the defects are injected, engineers shouldremove their own defectsdetermine the causes of their defectslearn to prevent those defectsFall 2005 CS 350/ODUThe Economics of QualitySoftware is the only modern technology that relies on testing to manage quality.With common quality practices, software groups typicallyspend 50+% of the schedule in testdevote more than half their resources to fixing defectscannot predict when they will finishdeliver poor-quality and over-cost productsTo manage cost and schedule, you must manage quality. To get a quality product out of test, you must put a quality product into test.Fall 2005 CS 350/ODU 7Testing Alone is IneffectiveOverloadHardware failureOperatorerrorData errorResourcecontentionConfigurationSafe and secure region = tested (shaded)Unsafe and insecure region = untested(black)Fall 2005 CS 350/ODURemoving Defects in TestWhen performing a task thousands of times, economics would suggest that you use the most efficient methods.A 50,000 LOC system with traditional development methods wouldhave 25+ defects/KLOC at test entry - 1250 defectstake 12,500+ programmer hours to testbe late and over budgetAt the typical rate of 10+ hours per defect, this is 6 programmer years.Fall 2005 CS 350/ODU 9Quality and Productivity100 developers40 hours x 50 weeks200,000 hours50% test time = 100,000 hours in testManaged quality = 60% increased team productivityCurrent MethodsManaged Quality100,000 for development2 LOC/hour = 200 KLOC20% test time = 40,000 hours of test160,000 for development2 LOC/hour = 320 KLOCFall 2005 CS 350/ODUDefect-removal Methods -1The principal ways to find and fix defects are by compilingunit testingintegration and system testingteam inspectionspersonal reviewsSince you will likely have to remove lots of defects, you should use the most efficient methods.Fall 2005 CS 350/ODUSource: Xerox110100100010000Time in MinutesDesignReviewDesignInspect.CodeReviewCodeInspect.UnitTestSystemTestDefect-removal Phase522225321405Defect-removal TimesFall 2005 CS 350/ODUDefect-removal Methods -2In a personal reviewyou privately review your productyour objective is to find and fix defects before testReviews are most effective when they are structured and measured.Use reviews for requirements, designs, code, and everything else that you develop.Also continue to use inspections, compiling, and testing.Fall 2005 CS 350/ODUDefect-removal Rates -1 Even at the personal level, it is more efficient to find defects in reviews than in testing.Unit test finds only about 2 to 4 defects per hour.Unit test finds about 50% of the defects.Code reviews find about 6 to 10 defects per hour.Practiced reviewers can find 70% or more of the defects before compiling or testing.Fall 2005 CS 350/ODUDefect-removal Rates -20510152025301 2 3 4 5 6 7 8 9 10Program NumberDefects Removed per HourCompileCRDLDRTest810 DevelopersFall 2005 CS 350/ODUWhy Reviews are EfficientIn testing, you must detect unusual behaviorfigure out what the test program was doingfind where the problem is in the programfigure out which defect could cause such behaviorThis can take a lot of time.With reviews and inspections, you follow your own logicknow where you are when you find a defectknow what the program should do, but did not know why this is a defectare in a better position to devise a correct fixFall 2005 CS 350/ODUReview PrinciplesPSP reviews follow a defined process with guidelines, checklists, and standards.The PSP review goal is to find every defect before the first compile or test.To address this goal, you shouldreview before compiling or testinguse coding standardsuse design completeness criteriameasure and improve your review processuse a customized personal checklistFall 2005 CS 350/ODUThe Code Review ChecklistYour reviews will be most effective when your personal checklist is customized to your own defect experience.Use your own data to select the checklist items.Gather and analyze data on the reviews.Adjust the checklist with experience.Do the reviews on a printed listing, not on the screen.The checklist defines the review steps and the suggested order for performing them. Review for one


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