Why and How to Control Cloning in Software Artifacts

215 Pages·2011·3.41 MB·English

Why and How to Control Cloning
in Software Artifacts
Elmar Juergens
Institut für Informatik
der Technischen Universität München
Why and How to Control Cloning
in Software Artifacts
Elmar Juergens
Vollständiger Abdruck der von der Fakultät für Informatik der Technischen Universität
MünchenzurErlangungdesakademischenGradeseines
DoktorsderNaturwissenschaften(Dr.rer.nat.)
genehmigtenDissertation.
Vorsitzender: Univ.-Prof. BerndBrügge,Ph.D.
PrüferderDissertation:
1. Univ.-Prof. Dr. Dr. h.c. ManfredBroy
2. Univ.-Prof. Dr. RainerKoschke
UniversitätBremen
DieDissertationwurdeam07.10.2010beiderTechnischenUniversitätMüncheneingere-
ichtunddurchdieFakultätfürInformatikam19.02.2011angenommen.

Abstract
The majority of the total life cycle costs of long-lived software arises after its first release, during
softwaremaintenance. Cloning,theduplicationofpartsofsoftwareartifacts,hindersmaintenance:
it increases size, and thus effort for activities such as inspections and impact analysis. Changes
need to be performed to all clones, instead of to a single location only, thus increasing effort. If
individual clones are forgotten during a modification, the resulting inconsistencies can threaten
programcorrectness. Cloningisthusaqualitydefect.
The software engineering community has recognized the negative consequences of cloning over
a decade ago. Nevertheless, it abounds in practice—across artifacts, organizations and domains.
Cloning thrives, since its control is not part of software engineering practice. We are convinced
that this has two principal reasons: first, the significance of cloning is not well understood. We
do not know the extent of cloning across different artifact types and the quantitative impact it has
onprogramcorrectnessandmaintenanceefforts. Consequently,wedonotknowtheimportanceof
clone control. Second, no comprehensive method exists that guides practitioners through tailoring
andorganizationalchangemanagementrequiredtoestablishsuccessfulclonecontrol. Lackingboth
aquantitativeunderstandingofitsharmfulnessandcomprehensivemethodsforitscontrol,cloning
islikelytobeneglectedinpractice.
This thesis contributes to both areas. First, we present empirical results on the significance of
cloning. Analysis of differences between code clones in productive software revealed over 100
faults. More specifically, every second modification to code that was done in unawareness of its
clones caused a fault, demonstrating the impact of code cloning on program correctness. Further-
more,analysisofindustrialrequirementsspecificationsandgraph-basedmodelsrevealedsubstantial
amountsofcloningintheseartifacts,aswell. Thesizeincreasecausedbycloningaffectsinspection
efforts—for one specification, by an estimated 14 person days; for a second one by over 50%. To
avoidsuchimpactonprogramcorrectnessandmaintenanceefforts,cloningmustbecontrolled.
Second,wepresentacomprehensivemethodforclonecontrol. Itcomprisesdetectortailoringtoim-
proveaccuracyofdetectedclones,andassessmenttoquantifytheirimpact. Itguidesorganizational
changemanagementtosuccessfullyintegrateclonecontrolintoestablishedmaintenanceprocesses,
and root cause analysis to prevent the creation of new clones. To operationalize the method, we
presentaclonedetectionworkbenchforcode,requirementsspecificationsandmodelsthatsupports
all these steps. We demonstrate the effectiveness of the method—including its tools—through an
industrialcasestudy,whereitsuccessfullyreducedcloningintheparticipatingsystem.
Finally,weidentifythelimitationsofclonedetectionandcontrol. Throughacontrolledexperiment,
we show that clone detection approaches are unsuited to detect behaviorally similar code that has
been developed independently and is thus not the result of copy & paste. Its detection remains an
importanttopicforfuturework.
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Acknowledgements
IhavespentthelastfouryearsasaresearcherattheLehrstuhlforSoftware&SystemsEngineering
at Technische Universität München from Prof. Dr. Dr. h. c. Manfred Broy. I want to express my
gratitudetoManfredBroyforthefreedomandresponsibilityIwasgrantedandforhisguidanceand
advice. Ihave,andstilldo,enjoyworkinginthechallengingandcompetitiveresearchenvironment
he creates. I want to thank Prof. Dr. rer. nat. Rainer Koschke for accepting to co-supervise this
thesis. I am grateful for inspiring discussions on software cloning, but also for the hospitality and
interest—bothbyhimandhisgroup—thatIexperiencedduringmyvisitinBremen. Myviewofthe
socialaspectsofresearch,whichformedinthelarge,thematicallyheterogenousgroupofManfred
Broy,wasenrichedbytheglimpseintothesmaller,morefocussedgroupofRainerKoschke.
Iamverygratefultomycolleagues. Theirsupport,bothonthescientificandonthepersonallevel,
wasvital forthesuccessof thisthesis. Andnot least, for mypersonaldevelopmentduring thelast
four years. I am grateful to Silke Müller for schedule magic. To Florian Deissenboeck for being
an example worth following and for both his encouragement and outright criticism. To Benjamin
Hummelforhismeritandcreativityinproducingideas,andforhisproductivityandeffectivenessin
their realization. To Martin Feilkas for his ability to overview and simplify complicated situations
and for reliability and trust come what may. To Stefan Wagner for his guidance and example in
scientificwritingandempiricalresearch. ToDanielRatiuforthesensitivity,carefulnessanddepth
heshowsduringscientificdiscussions(andoutsideofthem). ToLarsHeinemannforbeingthebest
colleague I ever shared an office with and for his tolerance exhibited doing so. To Markus Her-
rmannsdörfer for his encouragement and pragmatic, uncomplicated way that makes collaboration
productiveandfun. ToMarkusPizkaforraisingmyinterestinresearchandforencouragingmeto
startmyPhDthesis. Workingwithallofyouwas,andstillis,aprivilege.
Research, understanding and idea generation benefit from collaboration. I am grateful for joint
paper projects to Sebastian Benz, Michael Conradt, Florian Deissenboeck, Christoph Domann,
Martin Feilkas, Jean-François Girard, Nils Göde, Lars Heinemann, Benjamin Hummel, Klaus
Lochmann, Benedikt May y Parareda, Michael Pfaehler, Markus Pizka, Daniel Ratiu, Bernhard
Schaetz,JonathanStreit,StefanTeuchertandStefanWagner. Inaddition,thisthesisbenefitedfrom
the feedback of many. I am thankful for proof-reading drafts to Florian Deissenboeck, Martin
Feilkas, Nils Göde, Lars Heinemann, Benjamin Hummel, Klaus Lochmann, Birgit Penzenstadler,
DanielRatiuandStefanWagner. AndtoRebeccaTiarksforhelpwiththeBellonBenchmark.
Theempiricalpartsofthisworkcouldnothavebeenrealizedwithoutthecontinuoussupportofour
industrial partners. I want to thank everybody I worked with at ABB, MAN, LV1871 and Munich
ReGroup. IparticularlythankMunichReGroup—especiallyRainerJanßenandRudolfVaas—for
thelong-termcollaborationwithourgroupthatsubstantiallysupportedthisdissertation.
Mostofall,Iwanttothankmyfamilyfortheirunconditionalsupport(bothmaterialandimmaterial)
notonlyduringmydissertation,butduringallofmyeducation. Iamdeeplygratefultomyparents,
mybrotherand,aboveall,mywifeSofie.
5

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»Aman’sgottadowhataman’sgottado«
JohnCleeseinMontyPython’sGuidetoLife

Contents
1 Introduction 13
1.1 ProblemStatement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
1.2 Contribution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
1.3 Contents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
2 Fundamentals 19
2.1 NotionsofRedundancy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
2.2 SoftwareCloning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
2.3 NotionsofProgramSimilarity . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
2.4 TermsandDefinitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
2.5 CloneMetrics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
2.6 Data-flowModels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
2.7 CaseStudyPartners . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
2.8 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
3 State of the Art 37
3.1 ImpactonProgramCorrectness. . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
3.2 ExtentofCloning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
3.3 CloneDetectionApproaches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
3.4 CloneAssessmentandManagement . . . . . . . . . . . . . . . . . . . . . . . . . 47
3.5 LimitationsofCloneDetection . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
4 Impact on Program Correctness 53
4.1 ResearchQuestions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
4.2 StudyDesign . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
4.3 StudyObjects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
4.4 ImplementationandExecution . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
4.5 Results. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
4.6 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
4.7 ThreatstoValidity. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
4.8 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
5 Cloning Beyond Code 63
5.1 ResearchQuestions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
5.2 StudyDesign . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
5.3 StudyObjects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
5.4 ImplementationandExecution . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
9