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A Controlled Experiment in Maintenance Comparing Design Patterns to Simpler Solutions

A Controlled Experiment in Maintenance Comparing Design Patterns to Simpler Solutions. Fadi (Fad h i) Wedyan CS614 Spring 2007. Presentation Outlines. Introduction Objective Experiment setup Experiment Conduction Validity Threads Conclusions and Comments. Introduction.

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A Controlled Experiment in Maintenance Comparing Design Patterns to Simpler Solutions

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  1. A Controlled Experiment in Maintenance Comparing Design Patterns to Simpler Solutions Fadi (Fadhi) Wedyan CS614 Spring 2007

  2. Presentation Outlines • Introduction • Objective • Experiment setup • Experiment Conduction • Validity Threads • Conclusions and Comments

  3. Introduction • Design patterns aim to simplify maintenance and increase usability. • Design patterns increase flexibility and reduce coupling. • Design patterns increases program complexity in the case where the flexibility offered by the pattern is unnecessary.

  4. Objective • Investigate, with respect to maintenance time, whether it is useful to design programs with design patterns even if the actual problem is simpler than that solved by the design pattern. • Is the complexity introduced by the design pattern always justified?

  5. Experiment Setup • Four different programs, well-documented, written for the purpose of the experiment. • Two versions of each program are developed: Pattern version (PAT) and Alternative version (ALT). Implementation in C++. • Patterns implemented : ABSTRACT, FACTORY, COMPSITE, DECORATOR, FAÇADE, OBSERVER, and VISITOR.

  6. Experiment Setup, Cont’d • In each program, at least one of flexibility functionality offered by the design patterns is not needed by the maintenance tasks. • 29 subjects are used, all professional SE. - Some of them have theoretical or practical pattern knowledge. - Subjects are distributed into four balanced groups.

  7. Experiment Setup, Cont’d • Three Independent variables: • Programs and maintenance tasks. • Program version. • Amount of pattern knowledge. • Two dependent variables: • Time. • Correctness.

  8. Experiment Setup, Cont’d Table 1: Order of Programs Per Group

  9. Experiment Conduction • First Problem: Stock Ticker (ST) • Directs stocks to one or more displays. • Patterns: OBSERVER • Task 1: activate the second display unit. • Expectations: • E1: PRE-PAT Subjects require more time (supported) • E2: POST-PAT Subjects require less time. (Not Supported). • Conclusion: OBSERVER may be harmful!

  10. First Problem: Stock Ticker (ST), Cont’d • Task 2: Allow program to add new displays dynamically. • Expectations: • E3: PAT Subjects require less time (supported) • Conclusion: Nothing, unfair task? • Post and Pre are close for both programs

  11. Second Problem: Communication Channels (CO) • Pattern: DECORATOR for adding functionality. • Task 1: Enhancing functionality. • Expectations: • E1: PAT subjects are faster. (Supported) • E2: Pattern Knowledge enhance the ALT solution (Not supported) • Conclusions: • Patterns are preferable (time + correctness). • Positive effect of pattern use is independent of pattern knowledge.

  12. Second Problem: Communication Channels (CO), Cont’d • Task 2: Checking channel status • Expectations: • E1: ALT faster (Supported) • E2: ALT less errors (Not supported) • Conclusions: • Subjects were tired in the afternoon!

  13. Second Problem: Communication Channels (CO), Cont’d • Task 3: Create a channel with different functionality. • Expectations: • E1: ALT faster (Supported) • E2: ALT less errors (Not supported) • Conclusions: Harmful use of patterns? Or bad experiment?

  14. Third Problem: Graphics Library (GR) • Patterns: ABSRACT, FACTORY, COMPOSITE. • Task 1: Adding an output device type. • Expectations: • E1: ALT little faster (Supported) • E2: POST faster (supported) • Conclusions: ?

  15. Third Problem: Graphics Library (GR) • Task 2: Operation Sequence. • Expectations: • E3: No significant different (Supported) • E4: POST faster (not supported) • Conclusions: ?

  16. Forth Problem: Boolean Formulas (BO) • Patterns: VISITOR, COMPOSITE. • Task 1: Evaluating the formula • Expectation: • E1: PAT Faster (supported) • E2: POST Knowledge helps (supported)

  17. Validity Threads • Internal Threads • Group similarity • Time stamps. • External Threads • Original designers and implementers may be the ones who perform maintenance. • Real program are less documented. • Real maintainers implement and test their solutions. • Effect of other design patterns and/or variations.

  18. Conclusions • The use of design patterns is usually justified. • Common sense works! • Some times justified use of design pattern was harmful • Some times unjustified use of design patterns was useful

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