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:

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.

A software product possesses the characteristic completeness to the extent that all of its parts are present and each of its parts are 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.

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.

A software product possesses the characteristic portability to the extent that it can be operated easily and well on multiple computer configurations. Portability can mean both between different hardware setups--such as running on a Mac as well as a PC--and between different operating systems--such as running on both Mac OS X and GNU/Linux.

A software product possesses the characteristic consistency to the extent that it contains uniform notation, symbology and terminology within itself.

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.

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.

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).

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.

A software product possesses Structuredness to the extent that it possesses a definite pattern of organisation in its constituent parts. A software product written in a block-structured language such as Pascal will satisfy this characteristic.

A software product possesses the characteristic efficiency to the extent that it fulfills its purpose without waste of resources. This means resources in the sense of memory utilisation and processor speed.

A software product possesses the characteristic security to the extent that it is able to protect data against unauthorized access and to withstand malicious interference with its operations. Besides presence of appropriate security mechanisms such as authentication, access control and encryption, security also implies reliability in the face of malicious, intelligent and adaptive attackers.

User's perspective

In addition to the technical qualities of software, the end user's experience also determines the quality of software. This aspect of software quality is be called usability. It is hard to quantify the usability of a given software product. Some important questions to be asked are:

· Is the user interface intuitive?

· Is it easy to perform easy operations?

· Is it feasible to perform difficult operations?

· Does the software give sensible error messages?

· Do widgets behave as expected?

· Is the software well documented?

· Is the user interface self-explanatory/ self-documenting?

· Is the user interface responsive or too slow?

Also, the availability of (free or paid) support may determine the usability of software.