An empirical study of code clone genealogies

KimMiryung,; SazawalVibha,; NotkinDavid,; MurphyGail,

doi:10.1145/1095430.1081737

Cited by 199 publications

(209 citation statements)

References 33 publications

(22 reference statements)

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“…Kim et al studied the evolution of code clones over time (Kim et al 2005). In this study they grouped clones into clone classes and measured how often they were changed together over a series of CVS checkins.…”

Section: Related Workmentioning

confidence: 99%

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“Cloning considered harmful” considered harmful: patterns of cloning in software

2008

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Literature on the topic of code cloning often asserts that duplicating code within a software system is a bad practice, that it causes harm to the system's design and should be avoided. However, in our studies, we have found significant evidence that cloning is often used in a variety of ways as a principled engineering tool. For example, one way to evaluate possible new features for a system is to clone the affected subsystems and introduce the new features there, in a kind of sandbox testbed. As features mature and become stable within the experimental subsystems, they can be migrated incrementally into the stable code base; in this way, the risk of introducing instabilities in the stable version is minimized. This paper describes several patterns of cloning that we have observed in our case studies and discusses the advantages and disadvantages associated with using them. We also examine through a case study the frequencies of these clones in two medium-sized open source software systems, the Apache web server and the Gnumeric spreadsheet application. In this study, we found that as many as 71% of the clones could be considered to have a positive impact on the maintainability of the software system.

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Section: Related Workmentioning

confidence: 99%

“…Defining a set of evolutionary patterns based on the work of Kim et al (2005), they analyzed how maintenance activities affected clone classes. In particular, they investigated how and why some code clone classes change together and others did not.…”

Section: Related Workmentioning

confidence: 99%

“Cloning considered harmful” considered harmful: patterns of cloning in software

2008

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“…However, the cloning rate does increase steadily over time as observed by Li et al (2006) for the Linux kernel and FreeBSD, where again only certain subsystems closer to the hardware show a higher rate of copy and paste code. Kim et al analyzed the clone genealogy for two open-source Java systems using historical data from a version control system (Kim et al 2005). A clone genealogy forms a graph that shows how clones derive in time over multiple versions of a program from common ancestors.…”

Section: Clone Evolutionmentioning

confidence: 99%

Empirical evaluation of clone detection using syntax suffix trees

2008

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Reusing software through copying and pasting is a continuous plague in software development despite the fact that it creates serious maintenance problems. Various techniques have been proposed to find duplicated redundant code (also known as software clones). A recent study has compared these techniques and shown that token-based clone detection based on suffix trees is fast but yields clone candidates that are often not syntactic units. Current techniques based on abstract syntax trees-on the other hand-find syntactic clones but are considerably less efficient. This paper describes how we can make use of suffix trees to find syntactic clones in abstract syntax trees. This new approach is able to find syntactic clones in linear time and space. The paper reports the results of a large case study in which we empirically compare the new technique to other techniques using the Bellon benchmark for clone detectors. The Bellon benchmark consists of clone pairs validated by humans for eight software systems written in C or Java from different application domains. The new contributions of this paper over the conference paper are the additional analysis of Java programs, the exploration of an alternative path that uses parse trees instead of abstract syntax trees, and the investigation of the impact on recall and precision when clone analyses insist on consistent parameter renaming.

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“…Kim et al (2005) argue that aggressive refactoring is not worth the effort, as most clones are short lived. Also, they suggest that long lived clones may not be refactorable due to language limitations.…”

Section: Introductionmentioning

confidence: 99%

Clones: what is that smell?

2011

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Clones are generally considered bad programming practice in software engineering folklore. They are identified as a bad smell (Fowler et al. 1999) and a major contributor to project maintenance difficulties. Clones inherently cause code bloat, thus increasing project size and maintenance costs. In this work, we try to validate the conventional wisdom empirically to see whether cloning makes code more defect prone. This paper analyses the relationship between cloning and defect proneness. For the four medium to large open source projects that we studied, we find that, first, the great majority of bugs are not significantly associated with clones. Second, we find that clones may be less defect prone than non-cloned code. Third, we find little evidence that clones with more copies are actually more error prone. Fourth, we find little evidence to support the claim that clone groups that span more than one file or directory are more defect prone than collocated clones. Finally, we find that developers do not need to put a disproportionately higher effort to fix clone dense bugs. Our findings do not support the claim that clones are really a "bad smell" (Fowler et al. 1999). Perhaps we can clone, and breathe easily, at the same time.

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An empirical study of code clone genealogies

Cited by 199 publications

References 33 publications

“Cloning considered harmful” considered harmful: patterns of cloning in software

“Cloning considered harmful” considered harmful: patterns of cloning in software

Empirical evaluation of clone detection using syntax suffix trees

Clones: what is that smell?

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