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SOFTWARE QUALITY ASSURANCE

SOFTWARE QUALITY ASSURANCE. Basic Principles. Requirements. SW Quality : An issue in all phases of the life-cycle. System Design. Detailed Design. Implementation. Installation & Testing. Maintenance. SW Quality Factors. basic quality characteristics for whom?

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SOFTWARE QUALITY ASSURANCE

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  1. SOFTWARE QUALITY ASSURANCE Basic Principles

  2. Requirements SW Quality: An issue in all phases of the life-cycle System Design Detailed Design Implementation Installation & Testing Maintenance

  3. SW Quality Factors • basic quality characteristics • for whom? • depend on the phase of the life-cycle • quality measures? • consistency of the transformation process • mapping between phases • completeness and adequacy of the product • can the end-user use the product

  4. The Cost of SW Quality [B. Boehm] • quality costs time & money during development: • code and unit test: 8% • integration test: 7% • re-testing (after each fix): 20% • rework (in earlier phases): 10% ===> about 45% of your budget goes into quality related activities

  5. Cost Ratio of Errors Requirements : Maintenance = 1 : 200 ===> detect quality problems early

  6. The Benefits of SW Quality • lower maintenance cost • stable and useful product • satisfied customers • better chances for continuing releases • build corporate culture & identity • build know-how and expertise • better chances for SW and design reuse

  7. SW Quality Management • SRS must include quality specification • be precise & clear (“measurable”) • make clear what your priorities are • check at each milestone in your life-cycle • use reviews & tests • identify risks • decide on how to proceed

  8. Principle: Separation of Concerns development metrics quality metrics Project Management monitoring software & fixes SW Development Quality Assurance test & review reports

  9. The SOFTWARE QUALITYCHARACTERISTICSTREE

  10. SW Quality Characteristics - II[B. Boehm, A. Davis] • portability • reliability • efficiency • human engineering • maintainability • testability, understandability, modifiability

  11. Portability • The degree to which software running in one environment can easily be converted to run in another environment. • Specification & test: • very hard to quantify (time?) • specify indirectly by • limiting languages, compilers, tools, ... • insisting on good development methodology • (cohesion & coupling) • isolating environment dependent modules in your design • To whom and when is it important?

  12. Reliability • The ability of software to behave consistently in a user-acceptable manner (when running in stable and pre-planned environment). • Specification & test: • measure as a percentage: 99% reliability • of operational (time), functions, accuracy/integrity,... ? • MTTF (mean time to failure): • Does software degrade? • counting bugs (ratio): • a “post mortem”? • Bring “reliability” into perspective (cost).

  13. Efficiency • The level at which software uses and supports (scarce) resources. • Specification & test: • resource = capacity: specify in numbers. • resource = time: specify what time-frame you measure • stimulus - response • stimulus - stimulus ... • make sure your system is • device efficient and accountable • give rules for degradation of service • First design, then optimize.

  14. Human Engineering • User-friendliness and consistency in external behavior. The degree to which software reflects and integrates customer needs and culture. • Specification & test: • very hard to quantify • establish an authorized test/benchmark team • specify indirectly: • establish criteria for the user interface by providing rules for external system behavior, execution sequences, robustness, adaptability, ... • limit interactive styles, tools, languages, ...

  15. Maintainability • Based on three major qualities: • testability • understandability • modifiability • Specification & test: • specify indirectly by • insisting on good development methodology: evaluate your design with cohesion & coupling • provide for structured implementation environment: limit languages, compilers, tools, ... • A shared interest between customer and supplier.

  16. End of Section 4c coming up: forms of quality management

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