The Systems Life Cycle

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.

Life Cycle Phases

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:

1. Requirements analysis - in this stage, the scope of the system is defined, and a set of requirements is derived (i.e. the functionality and levels of service that the new system must provide). The requirements are then formally documented in a requirements specification, which forms the input to the design phase. The activities that take place in the analysis phase may include an initial feasibility study to determine whether the project justifies the resources required to complete it. The existing system will then be thoroughly investigated to determine what business processes are involved, the nature and volume of the data used, and the issues that need to be addressed by the new system.
2. Design - a system will be designed to meet the requirements specified as the result of the previous phase. The output of this phase will be a blueprint that is used by systems and software engineers to implement the hardware and software components for the new system. Some of the issues dealt with here include database design, the design of data entry screens, detailed software specifications, and system architecture.
3. Implementation - in this phase the system is actually built. Hardware is installed, database and software applications are written, and data is loaded into the system.
4. Testing - once the system is fully operational, it should be thoroughly tested before it is handed over to the client to ensure that all of the specified requirements have been met, and that the system is functioning correctly under operational conditions. Testing of individual system components (unit testing) is normally carried out throughout the implementation stage in order to correct any minor problems that may arise before they have a chance to escalate into major problems.
5. Maintenance - once the client has accepted the new system and it is in daily use, there will inevitably be adjustments to be made to the system throughout its useful life. Hardware elements will need to be replaced or upgraded, and the need for additional functionality or information processing features may necessitate modifications to software or database programs. Eventually, changes in the business environment in which the system must operate will create the need for a new system, and the cycle will begin again.

_{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.}