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软件工程实践者的研究方法chapter21课件WhyAreProjectsLate?•anunrealisticdeadlineestablishedbysomeoneoutsidethesoftwaredevelopmentgroup•changingcustomerr

equirementsthatarenotreflectedinschedulechanges;•anhonestunderestimateoftheamountofeffortand/orthenumberofres

ourcesthatwillberequiredtodothejob;•predictableand/orunpredictablerisksthatwerenotconsideredwhentheprojectcommenced;•technicaldifficultiesthatcou

ldnothavebeenforeseeninadvance;•humandifficultiesthatcouldnothavebeenforeseeninadvance;•miscommunicationamongprojectstaffthatresultsindelays

;•afailurebyprojectmanagementtorecognizethattheprojectisfallingbehindscheduleandalackofactiontocorrecttheprobl

emSchedulingPrinciples•compartmentalization—definedistincttasks•interdependency—indicatetaskinterrelationship•effortvalid

ation—besureresourcesareavailable•definedresponsibilities—peoplemustbeassigned•definedoutcomes—eachtaskmustEffortandDeliv

eryTimeEffortCostImpossibleregiontdEdTmin=0.75TdtoEoEa=m(td4/ta4)developmenttimeEa=effortinperson-mon

thstd=nominaldeliverytimeforscheduleto=optimaldevelopmenttime(intermsofcost)ta=actualdeliverytimedesiredEffortAllocation•―frontend‖activi

ties–customercommunication–analysis–design–reviewandmodification•constructionactivities–codingorcodegeneration•testingandinstallation–uni

t,integration–white-box,blackbox–regression40-50%30-40%15-20%DefiningTaskSets•determinetypeofproject•assessthedegreeofrigorrequired•identifyadaptat

ioncriteria•selectappropriatesoftwareengineeringtasksTaskSetRefinement1.1Conceptscopingdeterminestheoverallscopeoftheproject.Taskdefinition:Task1.1Co

nceptScoping1.1.1Identifyneed,benefitsandpotentialcustomers;1.1.2Definedesiredoutput/controlandinputevents

thatdrivetheapplication;BeginTask1.1.21.1.2.1FTR:ReviewwrittendescriptionofneedFTRindicatesthataformaltechnicalrev

iew(Chapter26)istobeconducted.1.1.2.2Derivealistofcustomervisibleoutputs/inputs1.1.2.3FTR:Reviewoutputs/inputswithcustomerandreviseas

required;endtaskTask1.1.21.1.3Definethefunctionality/behaviorforeachmajorfunction;BeginTask1.1.31.1.3.1F

TR:Reviewoutputandinputdataobjectsderivedintask1.1.2;1.1.3.2Deriveamodeloffunctions/behaviors;1.1.3.3FTR:Reviewfunctions/beha

viorswithcustomerandreviseasrequired;endtaskTask1.1.31.1.4Isolatethoseelementsofthetechnologytobeimplem

entedinsoftware;1.1.5Researchavailabilityofexistingsoftware;1.1.6Definetechnicalfeasibility;1.1.7Makequickestimateofsize;1.1.8CreateaScopeDefiniti

on;endTaskdefinition:Task1.1isrefinedtoDefineaTaskNetworkTimelineChartsTasksWeek1Week2Week3Week4WeeknTas

k1Task2Task3Task4Task5Task6Task7Task8Task9Task10Task11Task12UseAutomatedToolstoDeriveaTimelineChartSchedule

Tracking–conductperiodicprojectstatusmeetingsinwhicheachteammemberreportsprogressandproblems.–evalua

tetheresultsofallreviewsconductedthroughoutthesoftwareengineeringprocess.–determinewhetherformalprojectmilestones(thediamondsshowninFigure27.3)have

beenaccomplishedbythescheduleddate.–compareactualstart-datetoplannedstart-dateforeachprojecttasklistedinthebl(Fi274)ProgressonanOOProje

ct-I•Technicalmilestone:OOanalysiscompleted•Allclassesandtheclasshierarchyhavebeendefinedandreviewed.•Classattr

ibutesandoperationsassociatedwithaclasshavebeendefinedandreviewed.•Classrelationships(Chapter8)havebeenestablishedandreviewed.•Abehavio

ralmodel(Chapter8)hasbeencreatedandreviewed.•Reusableclasseshavebeennoted.•Technicalmilestone:OOdesigncompleted•Thesetof

subsystems(Chapter9)hasbeendefinedandreviewed.•Classesareallocatedtosubsystemsandreviewed.•Taskallocationhasbeenestablishedandreviewed.•Respon

sibilitiesandcollaborations(Chapter9)havebeenidentified.•Attributesandoperationshavebeendesignedandreviewed.•Thecommunicati

onmodelhasbeencreatedandreviewed.ProgressonanOOProject-II•Technicalmilestone:OOprogrammingcompleted•Eachnewclasshasbeenimplementedincodefromt

hedesignmodel.•Extractedclasses(fromareuselibrary)havebeenimplemented.•Prototypeorincrementhasbeenbuilt.•Tech

nicalmilestone:OOtesting•ThecorrectnessandcompletenessofOOanalysisanddesignmodelshasbeenreviewed.•Aclass-responsibility-collaborationnetwork(Chapt

er6)hasbeendevelopedandreviewed.•Testcasesaredesignedandclass-leveltests(Chapter19)havebeenconductedforeachclass.•Test

casesaredesignedandclustertesting(Chapter19)iscompletedandtheclassesareintegrated.•Systemleveltestshavebeencompleted.EarnedValueAnalysis(EVA)•Ear

nedvalue–isameasureofprogress–enablesustoassessthe―percentofcompleteness‖ofaprojectusingquantitativeanalysisratherthanrelyonagutfeeling–―providesac

curateandreliablereadingsofperformancefromasearlyas15percentintotheproject.‖[Fle98]ComputingEarnedValue-I•Thebudgetedcos

tofworkscheduled(BCWS)isdeterminedforeachworktaskrepresentedintheschedule.–BCWSiistheeffortplannedforworktaski.–Todet

ermineprogressatagivenpointalongtheprojectschedule,thevalueofBCWSisthesumoftheBCWSivaluesforallworkt

asksthatshouldhavebeencompletedbythatpointintimeontheprojectschedule.•TheBCWSvaluesforallworktasksaresummedtoderiv

ethebudgetatcompletion,BAC.Hence,BAC=∑(BCWSk)foralltaskskComputingEarnedValue-II•Next,thevalueforbudgetedcostofworkperformed(BCWP)i

scomputed.–ThevalueforBCWPisthesumoftheBCWSvaluesforallworktasksthathaveactuallybeencompletedbyapointintimeonthepr

ojectschedule.•―thedistinctionbetweentheBCWSandtheBCWPisthattheformerrepresentsthebudgetoftheactivitiesthatwereplannedtob

ecompletedandthelatterrepresentsthebudgetoftheactivitiesthatactuallywerecompleted.‖[Wil99]•GivenvaluesforBCWS,BAC,andBCWP,importantprogressi

ndicatorscanbecomputed:•Scheduleperformanceindex,SPI=BCWP/BCWS•Schedulevariance,SV=BCWP–BCWS•SPIisanindicationoft

heefficiencywithwhichtheprojectisutilizingscheduledresources.ComputingEarnedValue-III•Percentscheduledforcompletion=BCWS/BAC–providesa

nindicationofthepercentageofworkthatshouldhavebeencompletedbytimet.•Percentcomplete=BCWP/BAC–providesaquantitativeindicationofthepercentofcom

pletenessoftheprojectatagivenpointintime,t.•Actualcostofworkperformed,ACWP,isthesumoftheeffortactuallyexpendedonwork

tasksthathavebeencompletedbyapointintimeontheprojectschedule.Itisthenpossibletocompute•Costperformanceindex,CPI=BCWP/ACWP•Costvariance,C

V=BCWP–ACWP