Software Quality Factors

A software quality factor is a non-functional requirement for a software program which is not called up by the customer's contract, but nevertheless is a desirable requirement which enhances the quality of the software program.

Some software quality factors are listed here:

1) Understandability is possessed by a software product if the purpose of the product is clear. This goes further than just a statement of purpose - all of the design and user documentation must be clearly written so that it is easily understandable. This is obviously subjective in that the user context must be taken into account, i.e. if the software product is to be used by software engineers it is not required to be understandable to the layman.

2) A software product possesses the characteristic completeness to the extent that all of its parts are present and each of its parts is fully developed. This means that if the code calls a sub-routine from an external library, the software package must provide reference to that library and all required parameters must be passed. All required input data must be available.

3) A software product possesses the characteristic conciseness to the extent that no excessive information is present. This is important where memory capacity is limited, and it is important to reduce lines of code to a minimum. It can be improved by replacing repeated functionality by one sub-routine or function which achieves that functionality. It also applies to documents.

4) A software product possesses the characteristic portability to the extent that it can be operated easily and well on computer configurations other than its current one. This is particularly important with PC applications where, for example, a product is expected to work on all 80486 processors.

5) A software product possesses the characteristic maintainability to the extent that it facilitates updating to satisfy new requirements. Thus the software product which is maintainable should be well-documented, not complex, and should have spare capacity for memory usage and processor speed.

6) A software product possesses the characteristic testability to the extent that it facilitates the establishment of acceptance criteria and supports evaluation of its performance. Such a characteristic must be built-in during the design phase if the product is to be easily testable - a complex design leads to poor testability.

7) A software product possesses the characteristic usability to the extent that it is convenient and practicable to use. This is affected by such things as the human-computer interface. The component of the software which has most impact on this is the graphical user interface (GUI).

8) A software product possesses the characteristic reliability to the extent that it can be expected to perform its intended functions satisfactorily. This implies a time factor in that a reliable product is expected to perform correctly over a period of time. It also encompasses environmental considerations in that the product is required to perform correctly in whichever conditions it finds itself - this is sometimes termed robustness.