With respect to defining software quality, sometimes its helpful to look at software quality models as a framework of understanding. ISO 25010 outlines a flexible model with product/system quality –also known as internal and external quality (EQ)-, and system-in-use quality –also referred to as quality in use (QinU). Product quality consists of those characteristics that can be evaluated in early development stages, for instance, design documents, code quality, etc., while system quality consists of those characteristics and attributes that can be evaluated in late stages, with the application in execution state. On the other hand, system-in-use quality consists of characteristics as evaluated by an end user when actually executing application tasks in a real context. An example would be a nurse or a doctor entering patient record and diagnosis information into an electronic health records system. A doctor even while doing the same task, may have different error and completion rates than a nurse for whatever reason. Doctors may also take longer and have less efficiency in completing tasks simply because they don’t do as many. In addition, system QinU is heavily dependent on the context of the task and user. For instance, a user in a dim warehouse doing inventory will have a different viewpoint than a doctor in a well-lit hospital.

ISO 25010 also delineates a relationship between the two quality views whereby system quality ‘influences’ system-in-use quality and system-in-use quality ‘depends’ on system quality. We recently have developed 2Q2U version 2.0, which ties together all of these quality concepts by relating system quality characteristics and attributes with QinU and user experience (UX). Using 2Q2U, evaluators can select the quality characteristics to evaluate and conduct a systematic evaluation using the ‘depends’ and ‘influences’ relationships.