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Quality and Metrics

Quality and Metrics

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Quality and Metrics

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  1. Quality and Metrics One can't proceed from the informal to the formal by formal means. Alan J. Perlis

  2. Software Quality Flexibility Testability Portability Reusability Interoperability • Correctness • Reliability • Efficiency • Integrity • Usability • Maintainability 329-13

  3. McCall’s Software Quality Factors Portability Reusability Interoperability Maintainability Flexibility Testability PRODUCT REVISION PRODUCT TRANSITION PRODUCT OPERATION Correctness Usability Efficiency Reliability Integrity 329-13

  4. FURPS • Functionality • Usability • Reliability • Performance • Supportability ISO 9126 adds “Portability” 329-13

  5. Which is more important, • Correctness • Functionality 329-13

  6. Correctness • Does the system meet the documented requirements? • Functionality • Does the system meet the actual requirements of the users? • Are the written requirements the actual requirements of the users? 329-13

  7. Metrics • Metrics for “correctness” • # tests for each requirements • # tests that pass • # outstanding bugs • Metrics for “functionality” • ratings on a survey • average time to complete task on a prototype 329-13

  8. Metrics • Portability? • Reliability? • Supportability? • Flexibility? 329-13

  9. Evaluating Quality Method for evaluating quality should be • Simple and computable • Empirically and intuitively persuasive • Repeatable (objective) • Programming language independent • Effective for high-quality feedback 329-13

  10. Weighted Methods Per Class • Depth of Inheritance Tree • Number of Children • Coupling between Object Classes • Response for a Class • Lack of Cohesion in Methods 329-13

  11. Metrics for Software Quality Flexibility Testability Portability Reusability Interoperability • Correctness • Reliability • Efficiency • Integrity • Usability • Maintainability 329-13

  12. Feedback • Feedback is crucial, not necessarily numbers. • Design reviews, pair programming. If you don’t check to make sure that your software has a desired property, it doesn’t. 329-13

  13. Taking measurements • Manually • counting stories completed • man-months • Automatically • lines of code • number of classes 329-13

  14. Quality assurance plan • What are your goals for quality? • Define metrics • How will you tell whether you meet them? • Define process for taking measurements • What will you do if you don’t meet them? 329-13