What's the (function) point of Measurement?

It’s been more than 30 years since “function point analysis”  emerged in IT and yet most of the industry either: a) has never heard of it; b) has a misguided idea of what function points are; or c) was the victim of a botched software measurement program based on function points.

Today I’d simply like to clear up some common misconceptions about what function points are and what they are NOT. Future postings will get into the nuts and bolts of function points and how to use them, this is simply a first starting point.

What’s a function point?

A “function point” (FP) is a unit of measure that can be used to gauge the functional size of a piece of software.  (I published a primer on function points titled: Managing (the Size of) Your Projects – A Project Management Look at Function Points in the Feb 1999 issue of CrossTalk – the Journal of Defense Software Engineering from which I have excerpted here):

“FPs measure the size of a software project’s work output or work product rather than measure technology-laden features such as lines of code (LOC). FPs evaluate the functional user requirements that are supported or delivered by the software. In simplest terms, FPs measure what the software must do from an external, user perspective, irrespective of how the software is constructed. Similar to the way that a building’s square measurement reflects the floor plan size, FPs reflect the size of the  software’s functional user requirements…

However, to know only the square foot size of a building is insufficient to manage a construction project. Obviously, the construction of a 20,000 square-foot airplane hangar will be different from a 20,000 square-foot office building. In the same manner, to know only the FP size of a system is insufficient to manage a system development project: A 2,000 FP client-server financial project will be quite different from a 2,000 FP aircraft avionics project.”

In short function points are an ISO standardized measure that provides an objective number that reflects the size of what the software will do from an external “user” perspective (user is defined as any person, thing, other application software, hardware, department etc – anything that sends of receives data or uses data from the software).  Function points offer a common denominator for comparing different types of software construction whereby cost per FP and effort hours per FP can be determined.  This is similar to cost per square foot or effort per square foot in construction.  However, it is critical to know that function points are only part of what is needed to do proper performance measurement or project estimating.

To read the full article, click on the title Managing (the Size of) Your Projects – A Project Management Look at Function Points.

To your successful projects!


Carol Dekkers
email: dekkers@qualityplustech.com

Carol Dekkers provides realistic, honest, and transparent approaches to software measurement, software estimating, process improvement and scope management.  Call her office (727 393 6048) or email her (dekkers@qualityplustech.com) for a free initial consultation on how to get started to solve your IT project management and development issues.

For more information on northernSCOPE(TM) visit www.fisma.fi (in English pages) and for upcoming training in Tampa, Florida  — April 26-30, 2010, visit www.qualityplustech.com.

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Comments (2)

  1. Hi Carol,
    Good summary! Often function points seem to get confused with estimates. I always emphasize that it is another – non-trivial – story to derive effort from a particular number of function points.

    Regards, Michael

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