软件过程与管理chapter-16软件质量保证教学教材

1Chapter16软件质量保证齐大计控学院吴迪讨论软件质量保证为什么重要？3什么是软件质量？PhilCrosbyoncesaid:Theproblemofqualitymanagementisnotwhatpeopledon'tknowaboutit.Theproblemiswhattheythinktheydoknow...Inthisregard,qualityhasmuchincommonwithsex.Everybodyisforit.(Undercertainconditions,ofcourse.)Everyonefeelstheyunderstandit.(Eventhoughtheywouldn'twanttoexplainit.)Everyonethinksexecutionisonlyamatteroffollowingnaturalinclinations.(Afterall,wedogetalongsomehow.)And,ofcourse,mostpeoplefeelthatproblemsintheseareasarecausedbyotherpeople.(Ifonlytheywouldtakethetimetodothingsright.)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；6RoleoftheSQAGroup-IPreparesanSQAplanforaproject.TheplanidentifiesevaluationstobeperformedauditsandreviewstobeperformedstandardsthatareapplicabletotheprojectproceduresforerrorreportingandtrackingdocumentstobeproducedbytheSQAgroupamountoffeedbackprovidedtothesoftwareprojectteamParticipatesinthedevelopmentoftheproject’ssoftwareprocessdescription.

TheSQAgroupreviewstheprocessdescriptionforcompliancewithorganizationalpolicy,internalsoftwarestandards,externallyimposedstandards(e.g.,ISO-9001),andotherpartsofthesoftwareprojectplan.8RoleoftheSQAGroup-IIReviewssoftwareengineeringactivitiestoverifycompliancewiththedefinedsoftwareprocess.

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？1216.3.2SQAGoalsRequirementsquality.Thecorrectness,completeness,andconsistencyoftherequirementsmodelwillhaveastronginfluenceonthequalityofallworkproductsthatfollow.Designquality.Everyelementofthedesignmodelshouldbeassessedbythesoftwareteamtoensurethatitexhibitshighqualityandthatthedesignitselfconformstorequirements.Codequality.Sourcecodeandrelatedworkproducts(e.g.,otherdescriptiveinformation)mustconformtolocalcodingstandardsandexhibitcharacteristicsthatwillfacilitatemaintainability.Qualitycontroleffectiveness.Asoftwareteamshouldapplylimitedresourcesinawaythathasthehighestlikelihoodofachievingahighqualityresult.1416.5StatisticalSQAProduct&Processmeasurement...anunderstandingofhowtoimprovequality...CollectinformationonalldefectsFindthecausesofthedefectsMovetoprovidefixesfortheprocess1516.5StatisticalSQAInformationaboutsoftwareerrorsanddefectsiscollectedandcategorized.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。1716.5.2Six-SigmaforSoftwareEngineeringTheterm“sixsigma”isderivedfromsixstandarddeviations—3.4instances(defects)permillionoccurrences—implyinganextremelyhighqualitystandard.TheSixSigmamethodologydefinesthreecoresteps:Define

customerrequirementsanddeliverablesandprojectgoalsviawell-definedmethodsofcustomercommunicationMeasuretheexistingprocessanditsoutputtodeterminecurrentqualityperformance(collectdefectmetrics)Analyze

defectmetricsanddeterminethevitalfewcauses.Improve

theprocessbyeliminatingtherootcausesofdefects.Control

theprocesstoensurethatfutureworkdoesnotreintroducethecausesofdefects.1916.6SoftwareReliabilityAsimplemeasureofreliabilityismean-time-between-failure

(MTBF),where

MTBF=MTTF+MTTRTheacronymsMTTFandMTTRaremean-time-to-failure

and

mean-time-to-repair,respectively.Softwareavailabilityistheprobabilitythataprogramisoperatingaccordingtorequirementsatagivenpointintimeandisdefinedas

Availability=[MTTF/(MTTF+MTTR)]x100%2016.6.2SoftwareSafetySoftwaresafety

isasoftwarequalityassuranceactivitythatfocusesontheidentificationandassessmentofpotentialhazardsthatmayaffectsoftwarenegativelyandcauseanentiresystemtofail.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。22ISO