Software evolution and the staged model of the software lifecycle

Abstract

Abstract Software maintenance is concerned with modifying software once it has been delivered and has entered user service. Many studies have shown that maintenance is the dominant lifecycle activity for most practical systems; thus maintenance is of enormous industrial and commercial importance. Over the past 25 years or so, a conventional view of software development and maintenance has been accepted in which software is produced, delivered to the user, and then enters a maintenance stage. A review of this approach and the state of the art in research and practice is given at the start of the chapter. In most lifecycle models, software maintenance is lumped together as one phase at the end. In the experience of the authors, based on how maintenance is really undertaken (rather than how it might or should be done), software maintenance actually consists of a number of stages, some of which can start during initial development. This provides a very different perspective on the lifecycle. In the chapter, we introduce a new model of the lifecycle that partitions the conventional maintenance phase in a much more useful, relevant, and constructive way. It is termed the staged model. There are five stages through which the software and the development team progress. A project starts with initial development stage, and we then identify an explicit evolution stage. Next is a servicing stage, comprising simple tactical activities. Later still, the software moves to a phase-out stage in which no more work is done on the software other than to collect revenue from its use. Finally the software has a close-down stage. The key point is that software evolution is quite different and separate from servicing, from phase-out, and from close-down, and this distinction is crucial in clarifying both the technical and business consequences. We show how the new model can provide a coherent analytic approach to preserving software value. Finally, promising research areas are summarized.