The 2002 suite of ISO 9126 (Parts 1 to 4) addresses software quality from the
product perspective. Even though it is not exhaustive, this suite constitutes the
most extensive software quality model developed to date. The approach of its
quality model, initially published in 1991 and refined over the next ten years by
ISO's group of software engineering experts, is to represent quality as a whole set
of characteristics. This international standard divides software quality into six
general categories of characteristics: functionalities, reliability, usability,
effectiveness, maintainability and portability (Figure 2).