Aiding Comprehension of Cloning Through Categorization

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Aiding Comprehension of Cloning Through
Categorization

• Cory Kapser and Michael W. Godfrey
• Software Architecture Group
• School of Computer Science, University Of Waterloo

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Overview

• Motivation
• Background
• Methods
• Case Studies
• Results
• Discussion
• Summary

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Motivation

• Code duplication (cloning) is common in large,
  long-lived industrial software systems.
• Negatively affects successful system evolution!
• Thus, clone management or removal is desirable.

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Problems with clone detection technologies

• Comprehension
• Result sets often provide little information
  beyond its a clone
• Scalability
• VERY large result sets typical
• Accuracy
• Esp. false positives

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Proposed solution

• Classification of clones
• Improve comprehension through informative
  grouping and statistical analysis
• Improve scalability through easier navigation
• Improve accuracy through region-specific filtering

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Overview

• Motivation
• Background
• Methods
• Case Studies
• Results
• Discussion
• Summary

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Code cloning

• A serious problem in industrial software.
• Typically, 15 of a system is duplicated code.
• As high as 50 in some cases
• Ducasse

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Reasons for code cloning

• Perceived cost
• Time constraints
• Insufficient understanding of the underlying
  problem
• Architectural clarity

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Problems with clones

• Maintenance
• Size
• Comprehension
• Bugs (copied and new)
• Indication of poor design

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Managing clones

• Removal
• Documentation

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Overview

• Motivation
• Background
• Methods
• Case Studies
• Results
• Discussion
• Summary

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Our approach

• Perform clone detection
• Extract/define regions from source code
• Map clone pairs to regions
• Classify clones
• Filter clones
• Display results

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The taxonomy

• Classifies clones according to attributes such as
  location and region type of a clone
• Hierarchical

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ADD A SLIDE HERE

• To discuss what you hoped yoru taxonomy would
  help you with
• Why did you pcik that design?
• Give an example of how using this taxonomy could
  be helpful in a (simple, made up) example case

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Overview

• Motivation
• Background
• Methods
• Case Studies
• Results
• Discussion
• Summary

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Case studies

• PostgreSQL
• 543,387 LOC
• 1097 source files
• Linux kernel file-system subsystem
• 280,177 LOC
• 537 source files

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Filtering and classification results

• 85 87 of clones could be classified using the
  taxonomy
• Fewer unclassified clones in Same Directory
  Clones category
• Large percentage of false positives were removed
  via filtering structural and prototype regions.

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Overall cloning in the systems

• Function Clones dominate the Same Directory
  Clones.
• Most cloning occurs within the same directory.

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Frequency of clone types

• Very few loop clones
• Relatively many conditional clones
• 38 of the clone pairs in the Linux fs and 53 of
  the clone pairs of PostgreSQL made up function
  clones

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• It is possible to insert a table here with the
  results even if it is partial (to show that the
  work is there and that there are numbers)?
• Or maybe a graph? Nice to have this to imply
  heres all the hard work we did, boy did we
  sweat, and there are so many results that the
  obersvations are probably meaningful

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Overview

• Motivation
• Background
• Methods
• Case Studies
• Discussion
• Summary

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Cloning comprehension

• Classification of clones can improve
  comprehension
• User will have a working understanding of what a
  clone in a certain type means
• We believe navigation of the clone space will
  be greatly improved
• We now know more about cloning as it occurs in a
  software system
• Simple metrics are now available

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Tool support

• Clone Interpretation and Classification System
  (CICS)
• Provides GUI to navigate classified clones
• Will provide benchmarking support for clone
  detection tools
• Many features can be added complement the sorting
  of clones in the taxonomy

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CICS
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Overview

• Motivation
• Background
• Methods
• Case Studies
• Discussion
• Summary

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Summary

• Management of clones is important for the healthy
  evolution of a software system
• We can make the process of managing clones more
  comprehensible, scalable, and accurate

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Future work

• Deeper classification
• Benchmark suite
• IDE plugins
• Evolution of clones