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

This study generalizes some of the symptoms of ageing of a legacy system. Each symptom is specified by metrics and the results of the measurements made suggest what operations should be undertaken to renew the software. The study is based on retrospective analysis of data collected during the execution of a large renewal process of a very old legacy system. It therefore provides 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 increase their efficacy. It can also be used to define the reengineering requirements to ensure long life to the system despite successive evolutions of the application and the operation domain. The metrics can provide a basis for monitoring 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 to be performed to improve it. Finally, the paper points out the problems with renewal processes that still remain open. Copyright © 2001 John Wiley & Sons, Ltd.