Do We Measure Functional Size? Or Do We Count? Functional Sizing in View of the Metrology Standards

Functional Point counting has evolved into Functional Size Measurement. However, is it really a measurement? On the other hand, is this an imprecise change of name only? Measurements have a stray area, because no measurement instrument is completely exact. Counts in turn are exact. If a countable item does not go into the count, the count is imperfect but does not become a measurement. In this paper, we present today’s most popular counting methods and look in detail how they turn a function point count into functional size. We discuss SNAP, the Software Non-functional Assessment Process introduced by IFPUG that adds something like a quality size to software. We discuss the various other assessment processes that are likely to become important in the next few years, because they are urgently needed, such as security size assessments, privacy threat assessments and safety indices. All these are size assessments, which are quite different from functional size. The aim of software metrics has long focused on predicting the cost of software development projects. For this, in the past, functional size was dominant. Today, functionality is available from cloud services against cost per use, while other aspects such as privacy, security and safety will become dominant concerns when designing and implementing software service. This paper demonstrates how to use Six Sigma transfer functions for turning function point counts into measurements, be it functional, non-functional, safety, privacy, security or else.