Ageing of a data-intensive legacy system: symptoms and remedies

This study generalizes some of the symptoms of ageing of a legacy system. E ach symptom is specified by metrics and the results of the measurements mad e suggest what operations should be undertaken to renew the software. The s tudy is based on retrospective analysis of data collected during the execut ion of a large renewal process of a very old legacy system. It therefore pr ovides evidence of the expected efficacy of such renewal processes and can be used to decide how best to plan them and manage them in order to increas e their efficacy. It can also be used to define the reengineering requireme nts to ensure long fife to the system despite successive evolutions of the application and the operation domain. The metrics can provide a basis for m onitoring a software system to ensure that its quality does not degrade to such an extent that the most costly and risky renewal processes then have t o be performed to improve it. Finally, the paper points out the problems wi th renewal processes that still remain open. Copyright (C) 2001 John Wiley & Sons, Ltd.