Csmr08.ppt

Csmr08.ppt

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  Foutse Khomh andYann-Gaël Guéhéneuc © Khomh, 2008 Ptidej Team – OO Programs Quality Evaluation and Enhancement using Patterns Group of Open, Distributed Systems, Experimental Software Engineering Department of Informatics and Operations Research University of Montreal GEODES Do Design Patterns Impact Software Quality Positively? foutsekh@iro.umontreal.ca, guehene@iro.umontreal.ca CSMR'08
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  2/?? Context Design patterns (aspresented by the GoF) have been said to have a positive impact on quality characteristics – Expandability – Reusability – Understandability But, some studies presented counter-examples, i.e., Wendorff (Assessment of design patterns during software reengineering: Lessons learned from a large commercial project.)
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  3/?? Study Design (1/2) Hypothesis:“Design patterns have a positive impact on quality characteristics” Objective: prove or disprove the hypothesis with concrete evidence
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  4/?? Study Design (2/2) Requiredchoices – Quality characteristics – Kind of study Our choices – 10 quality characteristics related to design, implementation, and runtime – Empirical study (vs. absolute, vs. relative) • Manual activity • Developers' perception
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  5/?? Method Choice of designpatterns of interest – 23 design patterns in the GoF book Identification and definition of quality characteristics of interest – 10 characteristics Definition of a scale – Likert scale of 5 points + "I don't know" Generality Modularity at runtime Scalability Robustness Learnability Understandability Modularity Expandability Simplicity Reusability RuntimeImplementationDesign
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  6/?? Data Collection Questionnaire sendout to colleagues with a good knowledge of design patterns between January and May 2007 Questionnaire posted on mailing-lists refactoring@yahoogroups.com patterns-discussion@cs.uiuc.edu gang-of-4-patterns@cs.uiuc.edu
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  7/?? Data Processing Number ofreceived questionnaires: 30 – Number of complete questionnaires: 18 – Number of almost complete (90%) questionnaires: 2 – Incomplete questionnaires or with “I don't know”:10 Number of kept questionnaires: 20 Answers A and B aggregated in Positive, C in Neutral, and D and E in Negative – Some questionnaire were clearly generally more positive/negative than others
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  8/?? Results (1/2)
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  9/?? Results (2/2) We discussdetailed results – Three well-known design patterns • Composite • Abstract Factory • Flyweight – Three quality characteristics mentioned in the GoF • Reusability • Expandability • Understandability
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  10/?? Composite Overall positive impact onquality attributes Scalability and robustness not so positively impacted
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  11/?? Abstract Factory Overall neutral impacton quality attributes Expandability, generality, and modularity as expected Robustness surprising
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  12/?? Flyweight Overall negative impact onquality attributes Positive impact only on scalability as expected
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  13/?? Reusability Bridge Decorator Flyweight Command Interpreter State Visitor Builder Singleton Facade Mediator Memento Proxy A.Factory F.Method Prototype Adapter Composite Ch.Of.Resp. Iterator Observer Strategy T.Method NegativeNeutralPositive 10 positive impacts 6neutral impacts 7 negative impacts
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  14/?? Expandability SingletonFlyweight Memento Proxy A.Factory Builder F.Method Prototype Adapter Bridge Composite Decorator Facade Ch.Of.Resp. Command Interpreter Iterator Mediator Observer State Strategy T.Method Visitor NegativeNeutralPositive 19 positive impacts 3neutral impacts 1 negative impact
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  15/?? Understandability Decorator Flyweight Ch.Of.Resp. Command Visitor Proxy Memento T.Method A.Factory Builder F.Method Prototype Singleton Adapter Bridge Composite Facade Interpreter Iterator Mediator Observer State Strategy NegativeNeutralPositive 15 positive impacts 3neutral impacts 5 negative impacts
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  16/?? Null Hypothesis Test
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  17/?? Conclusion (1/2) Globally, designpatterns have a positive impact on quality attributes 16+ / 7- Simplicity 11+ / 12- Reusabilit y 14+ / 9- Learnabilit y 11+ / 12- Understandabilit y 19+ / 4-Number of Positive/Negative Patterns ExpandabilityQuality Characteristics 18+ / 5- Modularity 0+ / 23-1+ / 22-11+/ 12-19+ / 4-Number of Positive/Negative Patterns RobustnessScalabilityMod. at runtimeGeneralityQuality Characteristics
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  18/?? Conclusion (2/2) Pattern bypattern, their impact on quality varies and includes negative impact! So, design patterns do not always improve the quality of systems, thus they should be use with caution
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  19/?? Help Wanted Please helpus refine this study by downloading and filling in the questionnaire http://www.ptidej.net/downloads/