Do Crosscutting concerns cause defects?

1. Marc Eaddy, Thomas Zimmermann, Kaitlin Sherwood, VibhavGarg, Gail Murphy, NachiappanNagappan, Alfred Aho IEEE Transactions on Software Engineering July-Aug. 2008 Do Crosscutting concerns cause defects? Reviewed By: Paul Varcholik University of Central Florida pvarchol@ist.ucf.edu EEL 6883 – Software Engineering II Spring 2009

2. What is Crosscutting? • Implementation, of a concern, that is scattered across the program • A concern is any consideration that can impact the implementation of a program. • Features from a feature list • Requirements • Design patterns and design elements for a UML design document • Low-level programming concerns • Language • Coding Style • Algorithms

3. Research Question • How much does the amount that a concern is crosscutting affect the number of defects in a program? • Hypothesis The more scattered a concern’s implementation is, the more defects it will have, regardless of the implementation size. • Examined through three extensive case studies

4. Why Might Crosscutting Concerns Cause Defects? • A crosscutting concern is: • Harder to implement and modify • Multiple – possibly unrelated – locations in the code have to be found and updated simultaneously • Harder to understand • Developers must mentally untangle the code

5. Why Might Crosscutting Concerns Cause Defects? • Crosscutting first emerges when the developer creates – perhaps without realizing it – a concern implementation plan. • Maintainers may proceed without a full understanding of the scattered nature of the implementation.

6. Prior Work • Several empirical studies • Evidence that crosscutting concerns degrade code quality because they negatively impact internal quality metrics • Program size • Coupling • Separation of concerns (modularization)

7. Additional Terminology • A concern is scattered if it is related to multiple target elements. • A concern is tangled if both it and at least one other concern are related to the same target element.

8. Model • Concern – an item from a program’s non-executable specification • Program Elements • Classes • Fields • Methods • Defect – a software bug

9. Concern Metrics

10. Methodology • Reverse Engineer the concern-code mapping (subjective) • Mine thebug-code mapping • Infer the bug-concern mapping

11. Case Studies • Mylyn-Bugzilla • Eclipse plug-in • Rhino • JavaScipt/ECMAScript interpreter and compiler • iBATIS • Object-Relational mapping

12. Spearman Correlation Coefficients Range: -1.0 (a perfect negative correlation) to 1.0 (a perfect positive correlation)

13. Conclusion • All three studies showed a moderate-to-strong correlation between the degree of scattering and the number of defects. Concern scattering is correlated with defects. • But does it cause defects? Three criteria for causality: • Cause must precede the effect • A correlation must exist • The correlation must not be spurious

14. Strengths • Novel (appears to be first empirical study to examine crosscutting-defect correlation) • Well written • Solid statistical analysis • Technically sound methodology • Simple, but important, hypothesis

15. Weaknesses • Small study size (3 projects) • Human analyst for estimating concern-code mapping • Questionable techniques for identifying concerns(requirements) • Some misstatements in the paper • Do these results generalize? (e.g. across languages)

16. Final Thoughts • Study needs to be replicated • Can defects be reduced by reducing crosscutting? • Why does crosscutting occur? • Programming technology • Developer aptitude • Inherent complexity of the concern

17. Do Crosscutting Concerns Cause Defects? Marc Eaddy, Thomas Zimmermann, Kaitlin Sherwood, VibhavGarg, Gail Murphy, NachiappanNagappan, Alfred Aho IEEE Transactions on Software Engineering July-Aug. 2008 Reviewed By: Paul Varcholik University of Central Florida pvarchol@ist.ucf.edu EEL 6883 – Software Engineering II Spring 2009 Questions?