Mock-upexam2IMP25SoftwareevolutionThisisaclosed-bookexam.Nobooks,lecturenotes,slidesoranyauxiliarymaterialisallowed.Theexamconsistsoffivequestions;youshouldanswerfourofthem.Shouldyoudecidetoanswerallfivequestions,onlythefirstfourquestionswillbegraded.Whenansweringquestionstrytobebriefbutcomplete.

1. Softwaremetrics.a. (5)Giveadefinitionofcyclomaticcomplexity.Giveasmall

exampletoillustratethedefinition.b. (10)IntheoriginalpaperbyChidamberandKemererLCOM(C)

hasbeendefinedasP-QifP>Qand0,otherwise;wherePisthenumberofpairsofdistinctmethodsintheclassCthatdonotshareinstancevariables,andQisthenumberofpairsofdistinctmethodsintheclassCthatshareinstancevariables.

i. (2)Identifytheshortcomingsofthisdefinition.ii. (4)Proposeanalternativethatdoesnotsufferfromthe

shortcomingsidentified.iii. (4)Illustratethedifferencebetweentheoriginaldefinition

andtheoneproposedin1-b-iibymeansofanexample.c. (10)ThefollowingfigurefromBusingeetal.showsthemeanand

thestandarddeviationofthenormalizeddistancefromthemainsequenceDnoveranumberofrevisionsofPyDev.DescribetheevolutionofPyDevusingthisfigure.HereIwouldexpectthatyoutoatleastmakethefollowingobservationsandinterpretthem:

• Themeanislowerthanthestandarddeviation.ExplainwhatthiswouldmeanandhowwouldthisberelatedtothehistogramsofDndistributionyouhaveseenintheclass.

• Combinethepreviousobservationwiththerangeofthevaluesobserved(0.15-0.19).Whatwouldthismeanintermsofthe“mainsequence”?

• Trends.Ingeneralstandarddeviationseemstodecrease,whilethemeanismoreorlessstablebetweenJanuary2007andAugust2009.Howwouldyouexplainthisobservation?

• Singularities.Forinstance,inJanuary2007themeanhasgreatlyincreasedandaroundSeptember2009itdecreasedwhilethestandarddeviationremainedmoreorlessthesame.Whatcouldhavecausedthis?

2. Codeduplication.

a. (5)DefinethenotionofType2clones.Giveasmallexampletoillustratethedefinition.

b. (10)Comparethetoken-basedapproachofBrendaBaker’sandtheAST-basedapproachofIraBaxteretal.Whataretheadvantagesandthedisadvantagesofeachoneoftheapproaches?

c. (10)ThefollowingfigurefromLivierietal.showscloningbetweendifferentversionsoftheLinuxkernel.Thefigureisaheat-mapwithlowervaluesbeing“cold”(blue)andhighervaluesbeing“hot”(red).Thevaluevisualizedrepresentsthecoverageofthesourcecodeoftwoversionsbycodeshared(cloned)betweenthosetwoversions;thehigherthevaluethemoresimilarthoseversionsare.ThefigurehasbeenobtainedusingD-CCFinder,thedistributedversionoftheCCFindertooldiscussedintheclass.PleaseignorecharactersA,BandC.

DescribeevolutionoftheLinuxkernelbasedonthisfigure.

3. Repositorymining.a. (5)Giveadefinitionofadistributedversioncontrolsystem.Name

atleasttwodistributedversioncontrolsystems.b. (10)WhilesomeversioncontrolsystemssuchasCVSrecord

informationperfile,someotherssuchasSubversionrecorditpercommit.Whatareadvantages/disadvantagesofeachoneofthedecisions?

c. (10)ThefollowingfigurefromGîrbaetal.representstheownershipmapofJBoss(pleaseignorethecut-outpartintheleftuppercorner).DiscusstheevolutionoftheJBossdevelopers’communityandsystemorganizationbasedonthisfigure.

HereIwouldexpectyoutoobservethat(a)thecolor-mixchangeswiththetime,suggestingthatthedevelopers’teamcompositionhassignificantlychangedovertime(see,e.g.,appearanceanddisappearanceofthecyandeveloper),and(b)thechangesintheteamcompositionareaccompaniedbymanyfilesbeingadded(newlines)andremoved(linesstop)representingchangesinthesystemorganization---“newlords,newlaws”.

4. Architecturereconstructiona. (5)Theterm“reverseengineering”issometimesusedasa

synonymto“architecturereconstruction”.Explainthedifferencebetweenthetwotermsandgiveanexamplewhenoneofthetermsisapplicableandanotheroneisnot.

b. (10)ConsiderthefollowingexamplefromtheSoftwareMaintenancelecturenotesbyFranzWotawa,RoxaneKoitzandBirgitHofer.ConstructanObject-FlowGraphforthisexample.

Solution(pleaseignoretheannotations):

c. (10)Oneofthemajorproblemsrelatedtoanalysisofthe

reconstructedclassdiagramsisthelevelofdetail:automaticallyreconstructedclassdiagramscontainfartoomanydetailsforhumanstooversee.Presentatleasttwodifferenttechniquestotacklethisproblemanddiscusstheiradvantagesanddisadvantages.

5. Refactoring

a. (5)Giveadefinitionofrefactoringb. (10)Recalltheclassificationofrefactoringsbasedontheirimpact

ontheinterfaceasproposedbyMoonenetal.:compatible,backwardscompatible,canbemadebackwardscompatible,andincompatible.

i. (2*4)Foreachoneoftheclasses:giveanexampleofrefactoringbelongingtothisclass.Explainwhytherefactoringbelongstothisclass.

ii. (2)Furthermore,Moonenetal.haveidentifiedaseriesofsmellsinthetestcode,suchasTestrunwar(concurrentuseofresources)andMysteryguest(dependencyonanexternalresource).HowcanonerefactorthetestcodetoeliminatetheTestrunwarandMysteryguestsmells?

c. (10)Sokoletal.havestudiedtheimpactofrefactoringonsourcecodecomplexity,measuredintermsofthetotalcyclomaticcomplexityofaproject(CC).Theyhavedistinguishedbetween”documentedrefactorings”,i.e.,commitswithanassociatedmessagecontainingwordssuchas“refactoring”,“refactored”,“refactor”,andsoon;andremainingcommits.TheyhavestudiedJavaprojectsoftheApacheSoftwareFoundationandobservedthat1504documentedrefactoringsdecreasedcyclomaticcomplexity,1603didnotaffectitand3230increasedcyclomaticcomplexity.ThefollowingscatterplotshowsthepercentageofcommitsthatdecreasedCyclomaticComplexitybyeachproject’stotalcommitcount.Eachdotrepresentsaprojectandonlytheprojectswithdocumentedrefactoringswereconsidered.BasedonthisstudytheauthorsconcludethatnoevidencecanbefoundtosupportthepositiveeffectofrefactoringsontheCyclomaticComplexity.Whatkindofissuesmighthavethreatenedvalidityofthisconclusion?

Hereatleastthefollowingissuesshouldhavebeenmentioned:• Identificationof“documentedrefactorings”:theword

“refactoring”mightbemisusedbythedevelopers,e.g.,todenoteanykindofchange(“refactoredXXXtofixbugYYY”),makingtheapproachtoidentifyspuriousrefactorings,anddescriberefactoringswithoutusingtheword“refactoring”(“extractedmethodXXX”),makingtheapproachtomisstherefactorings.

• Codecommitsusuallyintegratemultiplechanges,someofthembeingrelatedtorefactoringandsomenotbeingrelatedtorefactoring,i.e.,attributingchangeinCCtorefactoringonlymightbepreposterous.

• Cyclomaticcomplexitymightnotbeanappropriatecomplexitymeasureforobject-orientedprograms;e.g.,itdoesnottakeinheritanceintoaccount.Moreover,getters/settersusuallyhavecyclomaticcomplexityofzero.

• ConclusionsfromtheApacheSoftwareFoundationsmightnotbegeneralizablebeyondtheprojectsofthisfoundation.Similarly,conclusionsfromtheJavaprojectsmightnotbegeneralizabletootherprogramminglanguages.

• Thedatasetshowshighvariance,i.e.,largedifferencesbetweendifferentprojects,i.e.,conclusionbasedonthecompletedatasetcannotbeappliedtoindividualprojects.