Every business information system development effort consists of a series of processes commonly known as a system development life cycle (SDLC) and is shown in Figure 1. Fundamentally, the four major phases are:
- Requirements, Analysis, and Design
- Detailed Design, Coding, and Unit Testing
- System Testing, Documentation, Training, and Acceptance Testing
- Implementation, Operation and Maintenance
In general, the resources required for each is a straight forward ratio of 1 to 4. That is, for every 1 unit of effort expended to complete the first phase, Requirements Analysis and Design, 4 additional units of effort are required for the remaining three life cycle phases. In total then, there are a total of five units of effort for the completion of the first implementation of the business information system.
This method of life cycle duration determination is not an alternative to the use of the Function Point count determination in other ROIs where the count of database tables, multiplied by 80 produces an approximation of the Function Points scope and size for a Business Information
System. Rather, this ROI's form of life cycle effort determination is merely the expression of the effort ratios between the first major phase and the remaining three phases.
Once a first implementation cycle of a business information system is completed and is set into production, maintenance begins almost immediately. That is because during the third phase, System Test, Documentation, Training, and Acceptance Testing, needed enhancements are invariably uncovered that were not accomplished because they were not identified as "show stoppers."
The first round of business information system enhancements are configured into a maintenance cycle that are almost always smaller-scale versions of all the phases. Thus, the maintenance cycle almost always has the Requirements through to Acceptance Testing subphases. Over a business information system's total life cycle, there are commonly five distinct iterations of maintenance cycles. These are illustrated in Figure 2, the Traditional Business Information System Life Cycle with Maintenance.
It is almost always the case that each maintenance cycle does not require the entire 5 units of effort that are required for the initial cycle. Thus, for each of these revision cycles, the quantity of unit efforts is not 5 but at most 1.25 (i.e., 25% of the original total effort). In total, across the entire life cycle of a business information system, the total unit efforts is thus: 5 units of effort for the initial production implementation effort plus five recycles of revision of 1.25 units each or a total of 11.25 units of effort
The issue here is to identify and set out a strategy that reduces the cost of the complete life cycle of a business information system. Regrettably, a common approach is to reduce the time for Requirements, Analysis, and Design. That approach however has two very negative side effects. First the work products are lower in quality, and second, not only will the quantity of changed work products be greater, but there will also be a larger quantity of maintenance cycles because second, third, and fourth order changes will not have been teased out through prototyping.