1. 1 SOFTWARE QUALITY ASSURANCE Basic Principles

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

3. 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. 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. 5 Cost Ratio of Errors Requirements : Maintenance = 1 : 200 ===> detect quality problems early

6. 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. 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. 8 Project Management SW DevelopmentQuality Assurance software & fixes test & review reports monitoring quality metricsdevelopment metrics Principle: Separation of Concerns

9. 9 The SOFTWARE QUALITY CHARACTERISTICS TREE

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

11. 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. 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. 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. 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. 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. 16 End of Section 4c coming up: forms of quality management