Multiple Viewpoints in Functional Size Measurement

Although there is broad agreement on the sorts of things to take into account when measuring functional size, there is a variety of opinion about how to do it. This is partly because several different views of functionality are addressed in functional size measurement. Some are better understood than others. In particular, the “general systems characteristics” (GSC’s) and “value adjustment factor” (VAF) are poorly understood. Our aim is to provide a foundation for research that may improve this aspect of functional size measurement. A survey of the evolution and state of practice of the GSC's and VAF leads us to identify various aspects of software that are important in functional size measurement. We relate these aspects of software to different views of functionality. A spectrum of viewpoints is seen, with core functionality at one end, effort estimation at the other, and different user viewpoints in between. By noting how the GSC’s and VAF contribute to these viewpoints, we see how value may be gained from them, and we identify directions for future research.