A system is considered to be a legacy system if it has been in operation for many years. A legacy system has many components. These include business processes, business rules, application software, application data, support software, and system hardware. The relationship among these components is shown in the following diagram.
The first component of the change control process is the Change Control Authority (CCA) or a Change Control Board (CCB). A CCA or CCB includes people from both developer and client side.
Whenever a change is required, the CCB decides whether to allow this change to happen or deny it. If it is decided that a change is needed, an Engineering Change Order or ECO is generated. An ECO defines the change to be made, the constraints that must be respected, and the criteria for review and audit. The change control process thus involves the following steps.