Metrics are usually computed at a low level:           classes, methods, …/ W&I / MDSE        3-11-2012 PAGE 0
Multitude of data values obscures a general      picture of the system maintainability/W&I / MDSE         3-11-2012 PAGE 1
That we are actually interested in!/W&I / MDSE          3-11-2012 PAGE 2
You Cant Control the Unfamiliar:A Study on the RelationsBetween AggregationTechniques for Software Metrics Bogdan Vasilesc...
Two kinds of aggregationSame metrics, different                Same artifact, differentartifacts                          ...
Various techniques can be   found in the literatureSame metrics, different                  Traditional: mean,artifacts   ...
Various techniques can be   found in the literatureSame metrics, different                  Traditional: mean,artifacts   ...
Questions      1. Which and to what extent do the different         aggregation techniques agree?      2. What is the natu...
Qualitas Corpus 20101126     • Qualitas Corpus 20101126r, 106 systems     • FitJava v1.1, 2 packages, 2240 SLOC     • NetB...
1) Agreement between diff techniques      • Agreement:          • Aggregation: Class SLOC  Package          • Techniques ...
1) Agreement: different inequality indices?     • Gini, Theil, Hoover, Atkinson – agree         • aggregates obtained conv...
1) Agreement: traditional and ineq indices?    • mean        • Kolm: strong (0,8) and statistically significant (92%)     ...
2) Nature of the relation: Typical patterns   • Theil is known to be more           • Linear relation with a “fat”     sen...
Which aggregation technique? (1)      • Theil, Hoover, Gini and Atkinson agree          • Any can be chosen from the corre...
Which aggregation technique? (2)      • Kolm and mean agree          • Kolm is reliable for skewed distributions          ...
Conclusions/W&I / MDSE         3-11-2012 PAGE 15
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  • Red line – mean, blue line – medianFurther approaches: distribution fitting, quality models (SIG, SQUALE)
  • Red line – mean, blue line – medianFurther approaches: distribution fitting, quality models (SIG, SQUALE)
  • % of the systems with statistically significant correlation between the corresponding indices at the 0.05 levelKendall correlation (rank based)
  • Icsm 2011 you can't control the unfamiliar

    1. 1. Metrics are usually computed at a low level: classes, methods, …/ W&I / MDSE 3-11-2012 PAGE 0
    2. 2. Multitude of data values obscures a general picture of the system maintainability/W&I / MDSE 3-11-2012 PAGE 1
    3. 3. That we are actually interested in!/W&I / MDSE 3-11-2012 PAGE 2
    4. 4. You Cant Control the Unfamiliar:A Study on the RelationsBetween AggregationTechniques for Software Metrics Bogdan Vasilescu Alexander Serebrenik Mark van den Brand
    5. 5. Two kinds of aggregationSame metrics, different Same artifact, differentartifacts metrics/W&I / MDSE 3-11-2012 PAGE 4
    6. 6. Various techniques can be found in the literatureSame metrics, different Traditional: mean,artifacts median, sum, … Econometric inequality indices: Gini, Theil, Hoover, Kolm, Atkinson/W&I / MDSE 3-11-2012 PAGE 5
    7. 7. Various techniques can be found in the literatureSame metrics, different Traditional: mean,artifacts median, sum, … Which aggregation Econometric technique inequality indices: Gini, Theil, Hoover, should we Kolm, Atkinson use?/W&I / MDSE 3-11-2012 PAGE 6
    8. 8. Questions 1. Which and to what extent do the different aggregation techniques agree? 2. What is the nature of the relation between the various aggregation techniques? 3. How does the correlation coefficient change as the systems evolve?/W&I / MDSE 3-11-2012 PAGE 7
    9. 9. Qualitas Corpus 20101126 • Qualitas Corpus 20101126r, 106 systems • FitJava v1.1, 2 packages, 2240 SLOC • NetBeans v6.9.1, 3373 packages 1890536 SLOC./W&I / MDSE 3-11-2012 PAGE 8
    10. 10. 1) Agreement between diff techniques • Agreement: • Aggregation: Class SLOC  Package • Techniques agree if they rank the packages similarly We use rank-based correlation coefficient: Kendall’s /W&I / MDSE 3-11-2012 PAGE 9
    11. 11. 1) Agreement: different inequality indices? • Gini, Theil, Hoover, Atkinson – agree • aggregates obtained convey the same information • Kolm does not!/W&I / MDSE 3-11-2012 PAGE 10
    12. 12. 1) Agreement: traditional and ineq indices? • mean • Kolm: strong (0,8) and statistically significant (92%) • median, standard deviation, and variance • sum • does not correlate with any other aggregation technique/W&I / MDSE 3-11-2012 PAGE 11
    13. 13. 2) Nature of the relation: Typical patterns • Theil is known to be more • Linear relation with a “fat” sensitive to the rich head • Theil increases faster when Gini increases/W&I / MDSE 3-11-2012 PAGE 12
    14. 14. Which aggregation technique? (1) • Theil, Hoover, Gini and Atkinson agree • Any can be chosen from the correlation point of view • Some might be “better” in each specific case • easy to interpret: Gini  [0,1] • provide additional insights: Theil (explanation) • negative values: Gini, Hoover − affects the domain! • sensitive for high values: Theil, Atkinson • deviations from uniformity: Gini, Hoover/ W&I / MDSE 3-11-2012 PAGE 13
    15. 15. Which aggregation technique? (2) • Kolm and mean agree • Kolm is reliable for skewed distributions − better alternative (“by no means”) • Not in the paper: − agreement observed for NOC − but not for DIT!/ W&I / MDSE 3-11-2012 PAGE 14
    16. 16. Conclusions/W&I / MDSE 3-11-2012 PAGE 15

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