This paper critically reviews the product quality model of ISO/IEC 25000 Series SQuaRE. This paper classifies the characteristics of the product quality model into intrinsic quality characteristics, contingency quality characteristics, and activity quality characteristics, which are defined as the evaluation criteria of the software product, contingencies which involve the product, and software activity performed on the product in the contingencies, respectively. This paper classifies activity quality characteristics into a hierarchy which can serve as a prototype of software activity quality model. This paper also classifies measures of the product quality model into those intrinsic, of contingency, and of activity. Discussions show that the measures do not properly specify the process to assign values to the corresponding characteristics. The results show well how useful it is to build a system of software quality models which consist with homogeneous items.