Abstract
The maintenance of existing software can account for 60 percent of all effort. expended by the resources used in the system development life cycle. To improve the situation, analysts must design systems that are easy to use and maintain at the early stage of the development process. At the design phase, an object-oriented system (o-o system) is decomposed into subjects. Each subject is decomposed into classes. A maintainable o-o system is a system where the change affects a less number of subjects. In this work, maintainability metric is proposed. This metric measures the localization of a change in a subject at the early stages of the development process during the analysis and design phases. This metric seems to be a good indicator of the quality of a system at the early stages.