Capturing Industrial Experiences of Software Maintenance Using Product Metrics

Many of successes in maintaining legacy software in Japan are due to low turnover rate of maintainers. However, future successes are not guaranteed because the wages system in Japan has begun changing and people are now getting to move between companies. Here, the organizations' demands for capturing and quantifying the maintainers' experiences in software evolution are growing much important today. Especially, an objective criterion for deciding whether a software module is to be reengineered or not is needed. Based on interviews to maintainers, this paper first illustrates maintainers' activity patterns, and, proposes a process model that can represent how maintainers' decisions affect maintainability of each software module. Then we introduce a snapshot model that maps software maintainability to product metrics. The snapshot model indicates a critical line – a criterion that can be used for deciding whether a module should be reengineered or not. We found that some of software metrics, measured from 20 years old system, fit the snapshot model; i.e., values of these metrics seem to be proportional to the degree of maintainability.