Sizing the Entire Development Process-Functional and Non-functional Perspectives

The single factor that best correlates with software development effort is size. This knowledge has led to the development of several size measurement methods, both ´physical´ and ´logical´. Although the functional size accounts for most of the effort variation, a large part of that variation is still unexplained by the functional size only. The lack of a standard way of dealing with non-functional factors led IFPUG to the idea of ´non-functional size´, a proposed measure of the impact of all non-functional factors over a software development project.