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    一篇关于软件可靠性度量的ppt讲稿,送给大家作为见面礼

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  • 软件可靠性
  • SoftwareReliability
    Measurement
    Measurement

    “Measurementistheprocessbywhichnumbersorsymbolsareassignedtoentitiesintherealworldinsuchawayastodescribethemaccordingtoclearlydefinedrules”

    Softwaremeasurement
    • Canmeasureoneofthreeentities:-
    processes-anysoftwarerelatedactivity;thesenormallyhaveatimefactor.Forinstance,design,testing,configurationmanagement,projectplanning,…
    products-anyartefacts,deliverablesordocumentswhichariseoutoftheprocesses.Examples-designdocuments,testplans,sourcecode,executablecode,usermanuals,…
    resources-itemswhichareinputstoprocesses,e.g.people,materials,money,…
    Productmeasurement
    QualityMetrics:-defectmetrics,designchanges,errorsincodeinspections,programtests,codechangesrequired
    ReliabilityMetrics:-hazardrate(i.e.probabilityoferrorinintervaldgiventhatithasnotfailedintimecostofrepairingfaults,probabilityofsoftwarefailure
    MaintainabilityMetrics:-relatedtocomplexitymeasures,readabilityofsourcecode
    Measuringreliability
    Canmeasure:-
    • MTTF-MeanTimeToFailure
    • MTTR-MeanTimeToRepair
    • MTBF-MeanTimeBetweenFailures= MTTF+MTTR
    Variousapproachesexist:-
    • Userandominputsandmeasuredefects
    • Carryoutcompleteobservation
    • Lookatindependentsetsoftests

    Reliabilitygrowth
    • Identifyandfixfaultsduringtestingandcollectdataconcerning,forexample,thetimebetweenfailuresofthesoftware
    • Usethisdatatopredicttimebetweenfailuresinthefuture
    • ReliabilityGrowthoccursasfaultsareremovedinthesoftwareanditsreliabilityincreases.Thetimebetweenfailuresgrowslonger.

    Reliabilitymeasures
    • Complexitymeasuresmayinfersomethingaboutthereliabilityofsoftwarebuttheycannotbeusedtoassurereliability.
    • Similarly,faultsordefectsinsoftwarecannotbeusedtopredictreliabilityastheymayormaynotleadtofailures.Somestudiesshowthatalargeproportionoffaultsneverleadtofailures.
    Reliabilitymeasures(ctd)
    • Thefrequencyofactualfailuresinthedevelopedsoftwareistheonlywaytopredictfuturereliablebehaviour.
    • Measurementstypicallyinvolverecordingthetimesbetweensuccessivefailuresofthesoftwarewhenitisexecutinginasimulatedoroperationalenvironment.
    Timeinmeasurement
    Measurementscanbetakenintermsof:-
    • ExecutionTime -theactualprocessingtimefortheexecutionoftheprogram
    • CalendarTime-thetimeinfamiliartermsofseconds,minutes,andhours.
    • ClockTime-thetimeacomputerisrunningwhileexecutingtheprogram.Otherprogramsmaybeexecutingonthesamemachineatthesametime.

    Trendanalysis
    • Requestforchange(RFC)-arequestputinbydevelopers,testers,qualityassurance,etc.tomodifythesoftware
    • DefectRate(DR)-thenumberofdefectsdetectedduringthetestingphase

    Analyzingtrends
    • Defectrateincreasesasmoremodificationstakeplace-thissuggeststhatreliabilitygrowthisnotoccurring
    • Asrequestsforchangestabilise,defectratedecreases-thissuggeststhatreliabilitygrowthisoccurring
    Reliabilitymodelling
    • Topredictreliability,currentfailuredataiscollectedandusedtoinferfuturebehaviour.
    • Examplesoftheuseofsuchpredictionsinclude:-
    – todetermineatwhatpointintimea particularlevelofreliabilitywillbe reached.
    – todeterminewhatlevelofreliabilitywill havebeenreachedbyacertainpointin time.

    Modelselection
    • Severalmodelshavebeendeveloped.However,thesehavetendedtogiveoftenlargelydifferentresultsforthesamedatasets.
    • Anappropriatemodelmustbeselectedaccordingtothecircumstancesandcontextandacertainamountofjudgementmustbeexercisedtodeterminewhichmodelisgivingreliableresults.

    Reliabilitycurve

    Hardwarereliability
    • HardwareandSoftwarereliabilityarebasedonsimilartheory,theintentionbeingthatreliabilitiescanbecombinedtogiveameasureofoverallsystemreliability.
    • Hardwarefailuresaretypicallyduetodeteriorationofmaterialsratherthanflawsindesign.Softwarefailuresaretypicallyduetodesignfaults.
    Comparinghardwareandsoftwarefailure
    • Hardwaredesignisseenasbeinglesscomplexthansoftwaredesign.
    • Forhardwareatraditionalbath-shapedcurveisappropriate
    • Softwarecanbereplicatedperfectlywhilethemanufacturingprocessforhardwaremayintroduceflaws.
    Onsoftwarereliability
    • Withsoftware,thereliabilitydoesnotalterwithtime.Assumingthestatedconditionsremainunaltered,thensoftwareisnotsubjecttorusting,corrosion,orwhateverandthatusuallysimplifiescalculationsconsiderably.Withhardwarethesituationisdifferent.
    • Softwarereliabilitymayfluctuateasitismodifiedandduringtestinganddebugging.Hardwareusuallyfollowsabath-tubshapedcurvewithaconstantreliabilityformostofitsoperationallife.

    Traditionalbath-shapedcurve:thehardwarepicture
    Commentsoncurve
    Thiscurveexhibitsthreedistinctphases:-
    • aninitialperiodduringwhichtimethesystemis’running-in’;duringthisperiodreliabilityoughttoincreaserapidlyandgraduallystabilise.
    • periodduringwhichthereisaconstantbutstablefailureratewhichiswellunderstood,expectedandcapableofbeinghandled.
    • awear-outperiodduringwhichthefailureratesincreasedramaticallyandexhibitscharacteristicswhichsuggestreplacement.
    Commentoninitialphase
    • Ofthesedifferentphases,theinitialrunning-inperiodcanusuallybereducedorevenremovedbyincreasingattentiontoqualitycontrol,tototalqualitymanagement,andtorelatedactivities.

    Commentsonhardwarehazards

    • Theanalysisoffailuresisimportantinordertounderstandthecausesandhelppreventfuturedisasters.
    • Overtheyears,surveyshavebeencarriedoutonthecausesofmetalfailure.Onesurveyrevealedthat:-
    – 55%offailureswerecausedbycorrosion.– 45%offailureswerecausedby mechanicalfailure
    Hazardsfrommovingmachinery
    • Anadditionalsetofhazardsarisewhenthereismovingmachinerypresentinasystem.
    • Thepresenceofsawsorrotatingdevicespresentaparticularlyacutesetofconcernsandleadtotheneedforguardsandsensorswhichcanautomaticallyswitchamachineoffifusedwrongly,andsoon.

    Lv.1
    不错,软件可靠性要好好学习一下!
    回复
    很不错的,谢谢,恭喜你成为软件可靠性的版主,英语很不错呀,我要好好跟你学习了. chinaxiayu
    回复
    英语看着有点头大,要慢慢看了。呵呵。。。。
    回复
    没中文?
    回复
    Lv.1
    3Q...................................................................
    回复
    明天多搞点标准给大家看看! :lol
    回复
    Lv.1
    ppt讲稿,以附件贴出就更好了,谢谢。
    回复
    谢谢
    回复

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