一篇关于软件可靠性度量的ppt讲稿,送给大家作为见面礼

christina_pc · 发表于 2007-4-6 10:03:22

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.

loveIT · 发表于 2007-4-6 13:06:20

不错，软件可靠性要好好学习一下！

chinaxiayu · 发表于 2007-4-6 22:27:52

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

reliability · 发表于 2007-4-10 09:24:10

英语看着有点头大，要慢慢看了。呵呵。。。。

fengguozun · 发表于 2007-11-30 22:35:25

没中文？

hmxjoke · 发表于 2008-1-22 14:26:57

3Q...................................................................

liqiangcondor · 发表于 2008-2-26 20:54:48

明天多搞点标准给大家看看！

njkkx · 发表于 2008-3-5 07:26:29

ppt讲稿，以附件贴出就更好了，谢谢。

所以。幸福 · 发表于 2018-3-10 15:03:17

谢谢

		自动登录	找回密码
密码			-注册-

一篇关于软件可靠性度量的ppt讲稿,送给大家作为见面礼

回复 #1 christina_pc 的帖子

浏览过的版块