《软件工程-实践者的研究方法》cha

TheseslidesaredesignedtoaccompanySoftwareEngineering:APractitionersApproach,7/e(McGraw-Hill,2009).Slidescopyright2009byRogerPressman.,1,Chapter11,QualityConcepts,SlideSettoaccompanySoftwareEngineering:APractitionersApproach,7/ebyRogerS.PressmanSlidescopyright1996,2001,2005,2009byRogerS.PressmanFornon-profiteducationaluseonlyMaybereproducedONLYforstudentuseattheuniversitylevelwhenusedinconjunctionwithSoftwareEngineering:APractitionersApproach,7/e.Anyotherreproductionoruseisprohibitedwithouttheexpresswrittenpermissionoftheauthor.AllcopyrightinformationMUSTappeariftheseslidesarepostedonawebsiteforstudentuse.,TheseslidesaredesignedtoaccompanySoftwareEngineering:APractitionersApproach,7/e(McGraw-Hill,2009).Slidescopyright2009byRogerPressman.,2,SoftwareQuality,In2005,ComputerWorldHil05lamentedthat“badsoftwareplaguesnearlyeveryorganizationthatusescomputers,causinglostworkhoursduringcomputerdowntime,lostorcorrupteddata,missedsalesopportunities,highITsupportandmaintenancecosts,andlowcustomersatisfaction.Ayearlater,InfoWorldFos06wroteaboutthe“thesorrystateofsoftwarequality”reportingthatthequalityproblemhadnotgottenanybetter.Today,softwarequalityremainsanissue,butwhoistoblame?Customersblamedevelopers,arguingthatsloppypracticesleadtolow-qualitysoftware.Developersblamecustomers(andotherstakeholders),arguingthatirrationaldeliverydatesandacontinuingstreamofchangesforcethemtodeliversoftwarebeforeithasbeenfullyvalidated.,TheseslidesaredesignedtoaccompanySoftwareEngineering:APractitionersApproach,7/e(McGraw-Hill,2009).Slidescopyright2009byRogerPressman.,3,Quality,TheAmericanHeritageDictionarydefinesqualityas“acharacteristicorattributeofsomething.”Forsoftware,twokindsofqualitymaybeencountered:Qualityofdesignencompassesrequirements,specifications,andthedesignofthesystem.Qualityofconformanceisanissuefocusedprimarilyonimplementation.Usersatisfaction=compliantproduct+goodquality+deliverywithinbudgetandschedule,TheseslidesaredesignedtoaccompanySoftwareEngineering:APractitionersApproach,7/e(McGraw-Hill,2009).Slidescopyright2009byRogerPressman.,4,QualityAPhilosophicalView,RobertPersigPer74commentedonthethingwecallquality:Quality.youknowwhatitis,yetyoudontknowwhatitis.Butthatsself-contradictory.Butsomethingsarebetterthanothers,thatis,theyhavemorequality.Butwhenyoutrytosaywhatthequalityis,apartfromthethingsthathaveit,itallgoespoof!Theresnothingtotalkabout.ButifyoucantsaywhatQualityis,howdoyouknowwhatitis,orhowdoyouknowthatitevenexists?Ifnooneknowswhatitis,thenforallpracticalpurposesitdoesntexistatall.Butforallpracticalpurposesitreallydoesexist.Whatelsearethegradesbasedon?Whyelsewouldpeoplepayfortunesforsomethingsandthrowothersinthetrashpile?Obviouslysomethingsarebetterthanothers.butwhatsthebetterness?.Soroundandroundyougo,spinningmentalwheelsandnowherefindinganyplacetogettraction.WhatthehellisQuality?Whatisit?,TheseslidesaredesignedtoaccompanySoftwareEngineering:APractitionersApproach,7/e(McGraw-Hill,2009).Slidescopyright2009byRogerPressman.,5,QualityAPragmaticView,Thetranscendentalviewargues(likePersig)thatqualityissomethingthatyouimmediatelyrecognize,butcannotexplicitlydefine.Theuserviewseesqualityintermsofanend-usersspecificgoals.Ifaproductmeetsthosegoals,itexhibitsquality.Themanufacturersviewdefinesqualityintermsoftheoriginalspecificationoftheproduct.Iftheproductconformstothespec,itexhibitsquality.Theproductviewsuggeststhatqualitycanbetiedtoinherentcharacteristics(e.g.,functionsandfeatures)ofaproduct.Finally,thevalue-basedviewmeasuresqualitybasedonhowmuchacustomeriswillingtopayforaproduct.Inreality,qualityencompassesalloftheseviewsandmore.,TheseslidesaredesignedtoaccompanySoftwareEngineering:APractitionersApproach,7/e(McGraw-Hill,2009).Slidescopyright2009byRogerPressman.,6,SoftwareQuality,Softwarequalitycanbedefinedas:Aneffectivesoftwareprocessappliedinamannerthatcreatesausefulproductthatprovidesmeasurablevalueforthosewhoproduceitandthosewhouseit.ThisdefinitionhasbeenadaptedfromBes04andreplacesamoremanufacturing-orientedviewpresentedinearliereditionsofthisbook.,TheseslidesaredesignedtoaccompanySoftwareEngineering:APractitionersApproach,7/e(McGraw-Hill,2009).Slidescopyright2009byRogerPressman.,7,EffectiveSoftwareProcess,Aneffectivesoftwareprocessestablishestheinfrastructurethatsupportsanyeffortatbuildingahighqualitysoftwareproduct.Themanagementaspectsofprocesscreatethechecksandbalancesthathelpavoidprojectchaosakeycontributortopoorquality.Softwareengineeringpracticesallowthedevelopertoanalyzetheproblemanddesignasolidsolutionbothcriticaltobuildinghighqualitysoftware.Finally,umbrellaactivitiessuchaschangemanagementandtechnicalreviewshaveasmuchtodowithqualityasanyotherpartofsoftwareengineeringpractice.,TheseslidesaredesignedtoaccompanySoftwareEngineering:APractitionersApproach,7/e(McGraw-Hill,2009).Slidescopyright2009byRogerPressman.,8,UsefulProduct,Ausefulproductdeliversthecontent,functions,andfeaturesthattheend-userdesiresButasimportant,itdeliverstheseassetsinareliable,errorfreeway.Ausefulproductalwayssatisfiesthoserequirementsthathavebeenexplicitlystatedbystakeholders.Inaddition,itsatisfiesasetofimplicitrequirements(e.g.,easeofuse)thatareexpectedofallhighqualitysoftware.,TheseslidesaredesignedtoaccompanySoftwareEngineering:APractitionersApproach,7/e(McGraw-Hill,2009).Slidescopyright2009byRogerPressman.,9,AddingValue,Byaddingvalueforboththeproduceranduserofasoftwareproduct,highqualitysoftwareprovidesbenefitsforthesoftwareorganizationandtheend-usercommunity.Thesoftwareorganizationgainsaddedvaluebecausehighqualitysoftwarerequireslessmaintenanceeffort,fewerbugfixes,andreducedcustomersupport.Theusercommunitygainsaddedvaluebecausetheapplicationprovidesausefulcapabilityinawaythatexpeditessomebusinessprocess.Theendresultis:(1)greatersoftwareproductrevenue,(2)betterprofitabilitywhenanapplicationsupportsabusinessprocess,and/or(3)improvedavailabilityofinformationthatiscrucialforthebusiness.,TheseslidesaredesignedtoaccompanySoftwareEngineering:APractitionersApproach,7/e(McGraw-Hill,2009).Slidescopyright2009byRogerPressman.,10,QualityDimensions,DavidGarvinGar87:PerformanceQuality.Doesthesoftwaredeliverallcontent,functions,andfeaturesthatarespecifiedaspartoftherequirementsmodelinawaythatprovidesvaluetotheend-user?Featurequality.Doesthesoftwareprovidefeaturesthatsurpriseanddelightfirst-timeend-users?Reliability.Doesthesoftwaredeliverallfeaturesandcapabilitywithoutfailure?Isitavailablewhenitisneeded?Doesitdeliverfunctionalitythatiserrorfree?Conformance.Doesthesoftwareconformtolocalandexternalsoftwarestandardsthatarerelevanttotheapplication?Doesitconformtodefactodesignandcodingconventions?Forexample,doestheuserinterfaceconformtoaccepteddesignrulesformenuselectionordatainput?,TheseslidesaredesignedtoaccompanySoftwareEngineering:APractitionersApproach,7/e(McGraw-Hill,2009).Slidescopyright2009byRogerPressman.,11,QualityDimensions,Durability.Canthesoftwarebemaintained(changed)orcorrected(debugged)withouttheinadvertentgenerationofunintendedsideeffects?Willchangescausetheerrorrateorreliabilitytodegradewithtime?Serviceability.Canthesoftwarebemaintained(changed)orcorrected(debugged)inanacceptablyshorttimeperiod.Cansupportstaffacquireallinformationtheyneedtomakechangesorcorrectdefects?Aesthetics.Mostofuswouldagreethatanaestheticentityhasacertainelegance,auniqueflow,andanobvious“presence”thatarehardtoquantifybutevidentnonetheless.Perception.Insomesituations,youhaveasetofprejudicesthatwillinfluenceyourperceptionofquality.,TheseslidesaredesignedtoaccompanySoftwareEngineering:APractitionersApproach,7/e(McGraw-Hill,2009).Slidescopyright2009byRogerPressman.,12,OtherViews,McCallsQualityFactors(SEPA,Section14.2.2)ISO9126QualityFactors(SEPA,Section14.2.3)TargetedFactors(SEPA,Section14.2.4),TheseslidesaredesignedtoaccompanySoftwareEngineering:APractitionersApproach,7/e(McGraw-Hill,2009).Slidescopyright2009byRogerPressman.,13,TheSoftwareQualityDilemma,Ifyouproduceasoftwaresystemthathasterriblequality,youlosebecausenoonewillwanttobuyit.Ifontheotherhandyouspendinfinitetime,extremelylargeeffort,andhugesumsofmoneytobuildtheabsolutelyperfectpieceofsoftware,thenitsgoingtotakesolongtocompleteanditwillbesoexpensivetoproducethatyoullbeoutofbusinessanyway.Eitheryoumissedthemarketwindow,oryousimplyexhaustedallyourresources.Sopeopleinindustrytrytogettothatmagicalmiddlegroundwheretheproductisgoodenoughnottoberejectedrightaway,suchasduringevaluation,butalsonottheobjectofsomuchperfectionismandsomuchworkthatitwouldtaketoolongorcosttoomuchtocomplete.Ven03,TheseslidesaredesignedtoaccompanySoftwareEngineering:APractitionersApproach,7/e(McGraw-Hill,2009).Slidescopyright2009byRogerPressman.,14,“GoodEnough”Software,Goodenoughsoftwaredelivershighqualityfunctionsandfeaturesthatend-usersdesire,butatthesametimeitdeliversothermoreobscureorspecializedfunctionsandfeaturesthatcontainknownbugs.Argumentsagainst“goodenough.”Itistruethat“goodenough”mayworkinsomeapplicationdomainsandforafewmajorsoftwarecompanies.Afterall,ifacompanyhasalargemarketingbudgetandcanconvinceenoughpeopletobuyversion1.0,ithassucceededinlockingthemin.Ifyouworkforasmallcompanybewaryofthisphilosophy.Ifyoudelivera“goodenough”(buggy)product,youriskpermanentdamagetoyourcompanysreputation.Youmaynevergetachancetodeliverversion2.0becausebadbuzzmaycauseyoursalestoplummetandyourcompanytofold.Ifyouworkincertainapplicationdomains(e.g.,realtimeembeddedsoftware,applicationsoftwarethatisintegratedwithhardwarecanbenegligentandopenyourcompanytoexpensivelitigation.,TheseslidesaredesignedtoaccompanySoftwareEngineering:APractitionersApproach,7/e(McGraw-Hill,2009).Slidescopyright2009byRogerPressman.,15,CostofQuality,PreventioncostsincludequalityplanningformaltechnicalreviewstestequipmentTrainingInternalfailurecostsincludereworkrepairfailuremodeanalysisExternalfailurecostsarecomplaintresolutionproductreturnandreplacementhelplinesupportwarrantywork,TheseslidesaredesignedtoaccompanySoftwareEngineering:APractitionersApproach,7/e(McGraw-Hill,2009).Slidescopyright2009byRogerPressman.,16,Cost,Therelativecoststofindandrepairanerrorordefectincreasedramaticallyaswegofrompreventiontodetectiontointernalfailuretoexternalfailurecosts.,TheseslidesaredesignedtoaccompanySoftwareEngineering:APractitionersApproach,7/e(McGraw-Hill,2009).Slidescopyright2009byRogerPressman.,17,QualityandRisk,“Peoplebettheirjobs,theircomforts,theirsafety,theirentertainment,theirdecisions,andtheirverylivesoncomputersoftware.Itbetterberight.”SEPA,Chapter1Example:ThroughoutthemonthofNovember,2000atahospitalinPanama,28patientsreceivedmassiveoverdosesofgammaraysduringtreatmentforavarietyofcancers.Inthemonthsthatfollowed,fiveofthesepatientsdiedfromradiationpoisoningand15othersdevelopedseriouscomplications.Whatcausedthistragedy?Asoftwarepackage,developedbyaU.S.company,wasmodifiedbyhospitaltechnicianstocomputemodifieddosesofradiationforeachpatient.,TheseslidesaredesignedtoaccompanySoftwareEngineering:APractitionersApproach,7/e(McGraw-Hill,2009).Slidescopyright2009byRogerPressman.,18,NegligenceandLiability,Thestoryisalltoocommon.Agovernmentalorcorporateentityhiresamajorsoftwaredeveloperorconsultingcompanytoanalyzerequirementsandthendesignandconstructasoftware-based“system”tosupportsomemajoractivity.Thesystemmightsupportamajorcorporatefunction(e.g.,pensionmanagement)orsomegovernmentalfunction(e