软件工程英文教学课件：Ch14 Quality Concepts

1Chapter14QualityConcepts

SoftwareEngineering:APractitioner’sApproach,7/e

byRogerS.Pressman2SoftwareQualityIn2005,ComputerWorld[Hil05]lamented(为…悲哀)that“badsoftwareplaguesnearlyeveryorganizationthatusescomputers,causinglostworkhoursduringcomputerdowntime,lostorcorrupteddata,missedsalesopportunities,highITsupportandmaintenancecosts,andlowcustomersatisfaction.Today,softwarequalityremainsanissue,butwhoistoblame(职责)?Customersblamedevelopers,arguingthatsloppy(粗心的)practicesleadtolow-qualitysoftware.Developersblamecustomers(andotherstakeholders),arguingthatirrational(非理性的)deliverydatesandacontinuingstreamofchangesforcethemtodeliversoftwarebeforeithasbeenfullyvalidated.3QualityTheAmericanHeritageDictionarydefinesqualityas“acharacteristicorattributeofsomething.”Forsoftware,twokindsofqualitymaybeencountered:Qualityofdesignencompassesrequirements,specifications,andthedesignofthesystem.Qualityofconformance(一致性)isanissuefocusedprimarilyonimplementation.Usersatisfaction=compliant(符合的)product+goodquality+deliverywithinbudgetandschedule4Quality—APhilosophical(辩证的)ViewQuality...youknowwhatitis,yetyoudon‘tknowwhatitis.Butthat’sself-contradictory(矛盾的).Somethingsarebetterthanothers,thatis,theyhavemorequality.Butwhenyoutrytosaywhatthequalityis,apartfromthethingsthathaveit,itallgoespoof!There'snothingtotalkabout.Ifyoucan'tsaywhatQualityis,howdoyouknowwhatitis,orhowdoyouknowthatitevenexists?Ifnooneknowswhatitis,thenforallpracticalpurposesitdoesn'texistatall.Butforallpracticalpurposesitreallydoesexist.5Quality—APragmatic(务实的)ViewTheuserviewseesqualityintermsofanend-user’sspecificgoals.Ifaproductmeetsthosegoals,itexhibitsquality.Themanufacturer’sview

definesqualityintermsoftheoriginalspecificationoftheproduct.Iftheproductconformstothespec,itexhibitsquality.Theproductviewsuggeststhatqualitycanbetiedtoinherent(内在的)characteristics(e.g.,functionsandfeatures)ofaproduct.Thevalue-basedviewmeasuresqualitybasedonhowmuchacustomeriswillingtopayforaproduct.Inreality,qualityencompassesalloftheseviewsandmore.6SoftwareQualitySoftwarequalitycanbedefinedas:Aneffectivesoftwareprocessappliedinamannerthatcreatesausefulproductthatprovidesmeasurablevalueforthosewhoproduceitandthosewhouseit.7EffectiveSoftwareProcessAneffectivesoftwareprocessestablishestheinfrastructurethatsupportsanyeffortatbuildingahighqualitysoftwareproduct.Softwareengineeringpracticesallowthedevelopertoanalyzetheproblemanddesignasolidsolution—bothcriticaltobuildinghighqualitysoftware.Umbrellaactivitiessuchaschangemanagementandtechnicalreviewshaveasmuchtodowithqualityasanyotherpartofsoftwareengineeringpractice.8UsefulProductAusefulproduct

deliversthecontent,functions,andfeaturesthattheend-userdesiresAusefulproductalwayssatisfiesthoserequirementsthathavebeenexplicitlystatedbystakeholders.Inaddition,itsatisfiesasetofimplicitrequirements(e.g.,easeofuse)thatareexpectedofallhighqualitysoftware.9AddingValueByaddingvalueforboththeproduceranduserofasoftwareproduct,highqualitysoftwareprovidesbenefitsforthesoftwareorganizationandtheend-usercommunity.Thesoftwareorganizationgainsaddedvaluebecausehighqualitysoftwarerequireslessmaintenanceeffort,fewerbugfixes,andreducedcustomersupport.Theusercommunitygainsaddedvaluebecausetheapplicationprovidesausefulcapabilityinawaythatexpeditessomebusinessprocess.10QualityDimensionsPerformanceQuality.Doesthesoftwaredeliverallcontent,functions,andfeaturesthatarespecifiedaspartoftherequirementsmodel?Featurequality.Doesthesoftwareprovidefeaturesthatsurpriseanddelightfirst-timeend-users?Reliability.Doesthesoftwaredeliverallfeaturesandcapabilitywithoutfailure?Doesitdeliverfunctionalitythatiserrorfree?Conformance(一致性).Doesthesoftwareconformtolocalandexternalsoftwarestandardsthatarerelevanttotheapplication?Durability(耐用性).Canthesoftwarebemaintained(changed)orcorrected(debugged)withoutthesideeffects?Willchangescausetheerrorrateorreliabilitytodegradewithtime?Serviceability.Canthesoftwarebemaintained(changed)orcorrected(debugged)inanacceptablyshorttimeperiod?Aesthetics.Mostofuswouldagreethatanaestheticentityhasauniqueflowandanobvious“presence”.11OtherViewsMcCall’sQualityFactors

(Section14.2.2)ISO9126QualityFactors

(Section14.2.3)TargetedFactors(Section14.2.4)12QualityDimensions-McCallmodelISO9126QualityModelISO/IEC9126质量模型是一种评价软件质量的通用模型，包括3个层次：质量特性、质量子特性、度量指标。ISO/IEC9126质量模型中六个质量特性与二十七个质量子特性的关系如下：13质量特性功能性可靠性易用性效率可维护性可移植性质量子特性适合性成熟性易理解性时间特性易分析性适应性准确性容错性易学性资源利用性易改变性易安装性互操作性易恢复性易操作性稳定性共存性保密安全性吸引性易测试性易替换性功能性的依从性可靠性的依从性易用性的依从性效率依从性维护性的依从性可移植性的依14CostofQualityPrevention(预防)costsincludequalityplanningformaltechnicalreviewstestequipmentInternalfailurecosts

includereworkrepairfailuremodeanalysisExternalfailurecostsarecomplaint(投诉)resolutionproductreturnandreplacementhelplinesupportWarranty(质保)work15CostTherelativeco