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The amount of effort needed to maintain a software system is related to the technical quality of the source code of that system. The ISO 9126 model for software product quality recognizes maintainability as one of the 6 main characteristics of software product quality, with adaptability, changeability, stability, and testability as subcharacteristics of maintainability. Remarkably, ISO 9126 does not provide a consensual set of measures for estimating maintainability on the basis of a system's source code. On the other hand, the maintainability index has been proposed to calculate a single number that expresses the maintainability of a system. In this paper, we discuss several problems with the MI, and we identify a number of requirements to be fulfilled by a maintainability model to be usable in practice. We sketch a new maintainability model that alleviates most of these problems, and we discuss our experiences with using such as system for IT management consultancy activities.
Heitlager et al. (Sat,) studied this question.