Harmonization of usability measurements in ISO9126 software engineering standards

The measurement of software usability is recommended in ISO 9126-2 to assess the external quality of software by allowing the user to test its usefulness before it is delivered to the client. Later, during the operation and maintenance phases, usability should be maintained, otherwise the software will have to be retired. This then raises harmonization issues about the proper positioning of the usability characteristic: does usability really belong to the external quality view of ISO 9126-2 and should the external quality characteristic of usability be harmonized with that of the quality in use model defined in ISO 9126-1 and ISO 9126-4? This paper analyzes these two questions: first, we identify and analyze the subset of ISO 9126-2 quality subcharacteristics and measures of usability that can be useful for quality in use, and then we recommend improvements to the harmonization of these ISO 9126 models