The term "system life cycle" can be applied to many kinds of endeavour, but in the context in which we are interested (information systems), it is used to describe the process by which an existing information system is replaced with another system. The idea of a 'life cycle' implies that the process has a beginning, an ending, and something going on in between.
Any new information system is carefully designed to fulfill a specific set of requirements, which are themselves derived only after a thorough investigation of the organisation's business needs. If correctly designed and implemented, the system should enable users of the system to be more productive, and management should see their business running more efficiently and profitably. Provided the system is adequately maintained and supervised, this situation may persist for a number of years, with the system doing everything that it was designed to do.
As time passes, however, many things will change. Technology evolves constantly. Personnel move on and are replaced. The business interests of the company may evolve and grow. Social, economic and environmental conditions change. The system that initially worked so well will begin to show its age. As its ability to adapt to new business requirements and changing conditions is taxed more and more, users will begin to become dissatisfied with system performance, and business efficiency will start to suffer. At this point, the life cycle of the current system is about to end, and that of a new system will begin.
Change, however, involves risk, especially in the field of IT. An alarming number of new IT systems fail to perform as specified, many are late, and many are over budget. A significant proportion of new systems fail to meet the requirements laid down for them, or are abandoned before they are complete. Many businesses neglect to properly train their staff in the use of new information systems, and many simply do not understand the capabilities and limitations of the technology. Currently, less than a fifth of all IT projects can claim to meet all of their objectives. In an effort to reduce the risk of failure, the systems life cycle breaks a project down into a series of well-defined stages, from the formulation of the initial concept through to the implementation and maintenance of a fully working system.
There are many lifecycle models in use. The number of phases, and the activities that take place within each phase, vary from one model to another. The generic phases outlined below, however, will appear in some form in most, if not all, of these models:
This article is an aggregation of two articles on the subject of the systems life cycle first published on the TechnologyUK.net website in January 2009.