Evaluating Product Quality


Why perform quality evaluation?
Many release and/or phase acceptance decisions are made with a degree of uncertainty since only hazy statements can be made about the results which are available. An unambiguous statement about results is only possible on the basis of a reasoned assessment of the object in question. This raises the question of the quality of the object.

What should we understand here as quality?
There is no such thing as good or bad quality in itself. Quality can only be evaluated on the basis of defined quality criteria. These result from the requirements made on the object.

Where are quality criteria obtained from?
Quality criteria can be drawn from a whole range of standpoints (from the user's perspective, from a maintenance perspective, etc.). It is also possible to define different degrees of quality fulfillment and/or metrics which allow the relevant criterion to be assessed. The quality (a term which in itself contains no quantity such as high, low, etc.) consists then of the degree to which it fulfils one or all of the criteria defined for the object. The quality may then satisfy (or not) the requirements as per the criteria.

What are quality criteria?
According to Siemens standard SN 77 350, the following quality features apply for software

  • Reliability
  • Degree to which it fulfils its defined function
  • User friendliness
  • Time response
  • Consumption behavior
  • Maintenance-friendliness
  • Portability

Within these features there are additional subfeatures such as learnability and usability (subfeatures of user-friendliness).

If these features are assigned values (e.g. point values, time values, etc.), the result is objective quality criteria.

How are evaluations performed?
Software can be evaluated against the prespecified quality criteria by

  • measurement
  • point rating
  • or other project-specific evaluation methods

This can take place, for example, after the corrections following on from reviews and tests ("the result is ready"). The evaluation result can constitute the reasoned basis for the release decision.

Where do I find out how to make a detailed quality evaluation?
The brochure 'Evaluation of Software Quality' (in German) is available from PSE QM. PSE QM QI provides advice on metrics.


Siemens AG Österreich, Program and Systems Engineering PSE
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Last modified: 08/27/98 15:42
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