軟件過程與管理chapter-16軟件質(zhì)量保證教學(xué)教材

1Chapter16軟件質(zhì)量保證齊大計(jì)控學(xué)院吳迪討論軟件質(zhì)量保證為什么重要？3什么是軟件質(zhì)量？PhilCrosbyoncesaid:Theproblemofqualitymanagementisnotwhatpeopledon'tknowaboutit.Theproblemiswhattheythinktheydoknow...Inthisregard,qualityhasmuchincommonwithsex.Everybodyisforit.(Undercertainconditions,ofcourse.)Everyonefeelstheyunderstandit.(Eventhoughtheywouldn'twanttoexplainit.)Everyonethinksexecutionisonlyamatteroffollowingnaturalinclinations.(Afterall,wedogetalongsomehow.)And,ofcourse,mostpeoplefeelthatproblemsintheseareasarecausedbyotherpeople.(Ifonlytheywouldtakethetimetodothingsright.)16.3.1軟件質(zhì)量保證的任務(wù)編制項(xiàng)目質(zhì)量保證計(jì)劃；參與項(xiàng)目的軟件過程的描述編寫；評(píng)審軟件工程活動(dòng)，以驗(yàn)證是否符合規(guī)定的軟件過程；審核指定的軟件工作產(chǎn)品以驗(yàn)證是否遵守作為軟件過程一部分的哪些規(guī)定。確保根據(jù)文檔化的規(guī)程記錄和處理軟件工作和工作產(chǎn)品中的偏差；記錄各種不符合項(xiàng)報(bào)告給高層管理人員；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.討論如果客戶不斷改變他想做的事情，是否還有可能評(píng)估軟件質(zhì)量？為什么軟件工程小組與獨(dú)立的軟件質(zhì)量保證小組的關(guān)系經(jīng)常是緊張的？這種緊張關(guān)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.已經(jīng)證明統(tǒng)計(jì)軟件質(zhì)量保證技術(shù)確實(shí)質(zhì)量提高，某些情況下，軟件組織已經(jīng)去得了每年減少51%缺陷的好成績(jī)。統(tǒng)計(jì)SQA及Pareto原則的應(yīng)用可以概括：把時(shí)間用在真正重要的地方，但是首先你必須知道什么重要。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.討論和作業(yè)一個(gè)正確的程序還能不可靠嗎？一個(gè)正確的程序還能不表現(xiàn)高質(zhì)量嗎？除了統(tǒng)計(jì)錯(cuò)誤和缺陷外，還有那些軟件特征具有質(zhì)量意義？給出兩個(gè)安全性至關(guān)重要的計(jì)算機(jī)控制系統(tǒng)，并為每個(gè)系統(tǒng)列出至少3條與軟件失效直接相關(guān)的災(zāi)難。22ISO