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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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Presentation Transcript
slide2

Requirements

SW Quality:

An issue in all phases

of the life-cycle

System Design

Detailed Design

Implementation

Installation & Testing

Maintenance

sw quality factors
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
the cost of sw quality b boehm
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

cost ratio of errors
Cost Ratio of Errors

Requirements : Maintenance

=

1 : 200

===> detect quality problems early

the benefits of sw quality
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
sw quality management
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
slide8

Principle: Separation of Concerns

development metrics

quality metrics

Project Management

monitoring

software & fixes

SW Development

Quality Assurance

test & review reports

sw quality characteristics ii b boehm a davis
SW Quality Characteristics - II[B. Boehm, A. Davis]
  • portability
  • reliability
  • efficiency
  • human engineering
  • maintainability
    • testability, understandability, modifiability
portability
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?
reliability
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).
efficiency
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.
human engineering
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, ...
maintainability
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.
end of section 4c
End of Section 4c

coming up:

forms of

quality management