软件过程与管理chapter_16软件质量保证.ppt

1,Chapter16,软件质量保证,讨论,软件质量保证为什么重要？,3,什么是软件质量？,PhilCrosbyoncesaid:Theproblemofqualitymanagementisnotwhatpeopledontknowaboutit.Theproblemiswhattheythinktheydoknow.Inthisregard,qualityhasmuchincommonwithsex.Everybodyisforit.(Undercertainconditions,ofcourse.)Everyonefeelstheyunderstandit.(Eventhoughtheywouldntwanttoexplainit.)Everyonethinksexecutionisonlyamatteroffollowingnaturalinclinations.(Afterall,wedogetalongsomehow.)And,ofcourse,mostpeoplefeelthatproblemsintheseareasarecausedbyotherpeople.(Ifonlytheywouldtakethetimetodothingsright.),4,16.2ElementsofSQA,StandardsReviewsandAuditsTestingError/defectcollectionandanalysisChangemanagementEducationVendormanagementSecuritymanagementSafetyRiskmanagement,16.3.1软件质量保证的任务,编制项目质量保证计划；参与项目的软件过程的描述编写；评审软件工程活动，以验证是否符合规定的软件过程；审核指定的软件工作产品以验证是否遵守作为软件过程一部分的哪些规定。确保根据文档化的规程记录和处理软件工作和工作产品中的偏差；记录各种不符合项报告给高层管理人员；,6,RoleoftheSQAGroup-I,PreparesanSQAplanforaproject.TheplanidentifiesevaluationstobeperformedauditsandreviewstobeperformedstandardsthatareapplicabletotheprojectproceduresforerrorreportingandtrackingdocumentstobeproducedbytheSQAgroupamountoffeedbackprovidedtothesoftwareprojectteam,Participatesinthedevelopmentoftheprojectssoftwareprocessdescription.TheSQAgroupreviewstheprocessdescriptionforcompliancewithorganizationalpolicy,internalsoftwarestandards,externallyimposedstandards(e.g.,ISO-9001),andotherpartsofthesoftwareprojectplan.,8,RoleoftheSQAGroup-II,Reviewssoftwareengineeringactivitiestoverifycompliancewiththedefinedsoftwareprocess.identifies,documents,andtracksdeviationsfromtheprocessandverifiesthatcorrectionshavebeenmade.,Auditsdesignatedsoftwareworkproductstoverifycompliancewiththosedefinedaspartofthesoftwareprocess.reviewsselectedworkproducts;identifies,documents,andtracksdeviations;verifiesthatcorrectionshavebeenmadeperiodicallyreportstheresultsofitsworktotheprojectmanager.,Ensuresthatdeviationsinsoftwareworkandworkproductsaredocumentedandhandledaccordingtoadocumentedprocedure.Recordsanynoncomplianceandreportstoseniormanagement.Noncomplianceitemsaretrackeduntiltheyareresolved.,讨论,如果客户不断改变他想做的事情，是否还有可能评估软件质量？为什么软件工程小组与独立的软件质量保证小组的关系经常是紧张的？这种紧张关系是否是正常的？,12,16.3.2SQAGoals,Requirementsquality.Thecorrectness,completeness,andconsistencyoftherequirementsmodelwillhaveastronginfluenceonthequalityofallworkproductsthatfollow.Designquality.Everyelementofthedesignmodelshouldbeassessedbythesoftwareteamtoensurethatitexhibitshighqualityandthatthedesignitselfconformstorequirements.,Codequality.Sourcecodeandrelatedworkproducts(e.g.,otherdescriptiveinformation)mustconformtolocalcodingstandardsandexhibitcharacteristicsthatwillfacilitatemaintainability.Qualitycontroleffectiveness.Asoftwareteamshouldapplylimitedresourcesinawaythathasthehighestlikelihoodofachievingahighqualityresult.,14,16.5StatisticalSQA,Product&Process,measurement,.anunderstandingofhow,toimprovequality.,CollectinformationonalldefectsFindthecausesofthedefectsMovetoprovidefixesfortheprocess,15,16.5StatisticalSQA,Informationaboutsoftwareerrorsanddefectsiscollectedandcategorized.Anattemptismadetotraceeacherroranddefecttoitsunderlyingcause.UsingtheParetoprinciple(80percentofthedefectscanbetracedto20percentofallpossiblecauses),isolatethe20percent(thevitalfew).Oncethevitalfewcauseshavebeenidentified,movetocorrecttheproblemsthathavecausedtheerrorsanddefects.,已经证明统计软件质量保证技术确实质量提高，某些情况下，软件组织已经去得了每年减少51%缺陷的好成绩。统计SQA及Pareto原则的应用可以概括：把时间用在真正重要的地方，但是首先你必须知道什么重要。,17,16.5.2Six-SigmaforSoftwareEngineering,Theterm“sixsigma”isderivedfromsixstandarddeviations3.4instances(defects)permillionoccurrencesimplyinganextremelyhighqualitystandard.TheSixSigmamethodologydefinesthreecoresteps:Definecustomerrequirementsanddeliverablesandprojectgoalsviawell-definedmethodsofcustomercommunication,Measuretheexistingprocessanditsoutputtodeterminecurrentqualityperformance(collectdefectmetrics)Analyzedefectmetricsanddeterminethevitalfewcauses.Improvetheprocessbyeliminatingtherootcausesofdefects.Controltheprocesstoensurethatfutureworkdoesnotreintroducethecausesofdefects.,19,16.6SoftwareReliability,Asimplemeasureofreliabilityismean-time-between-failure(MTBF),whereMTBF=MTTF+MTTRTheacronymsMTTFandMTTRaremean-time-to-failureandmean-time-to-repair,respectively.SoftwareavailabilityistheprobabilitythataprogramisoperatingaccordingtorequirementsatagivenpointintimeandisdefinedasAvailability=MTTF/(MTTF+MTTR)x100%,20,16.6.2SoftwareSafety,Softwaresafetyisasoftwarequalityassuranceactivitythatfocusesontheidentificationandassessmentofpotentialhazardsthatmayaffectsoftwarenegativelyandcauseanentiresystemtofail.Ifhazardscanbeidentifiedearlyinthesoftwareprocess,softwaredesignfeaturescanbespecifiedthatwilleithereliminateorcontrolpotentialhazards.,讨论和作业,一个正确的程序还能不可靠吗？一个正确的程序还能不表现高质量吗？除了统计错误和缺陷外，还有那些软件特征具有质量意义？给出两个安全性至关重要的计算机控制系统，并为每个系统列出至少3条与软件失效直接相关的灾难。,22,ISO9001:2000Standard,ISO9001:2000isthequalityassurancestandardthatappliestosoftwareengineering.Thestandardcontains20requirementsthatmustbepresentforaneffectivequalityassurancesystem.TherequirementsdelineatedbyISO9001:2000addresstopicssuchasmanagementresponsibil