In this paper, we discuss the experiences gained in a large-scale industrial reengineering project. The subject system is a medical data management software that has been continuously developed and maintained for about twenty years. About four years ago, it has been decided to subsequently reimplement the entire system in Java, while continuing maintenance of the legacy system.

The focus of this paper is less on technical details concerning reverse engineering tools, but rather on the overall approach for reengineering a large and complex legacy system. Central issues are the identification and definition of a suitable software development process, training for the developers, as well as the ongoing reverse engineering of the existing system. The latter has been carried out in parallel to continuous maintenance of both the legacy system and the reimplementation.