An Introduction to FPA

Keywords Function Point Analysis (FPA) software engineering software measure
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In 1979, Allan Albrecht of IBM developed the Function Point Analysis (FPA) in
response to a number of problems with other system size measures, such as lines of
codes. Before the launch of FPA, the “Lines of Code” method could be considered as
one of the main measurement techniques for system size. However, its results varied
greatly depending on programming languages used. It was also not applicable at the
early stage of the development life cycle.
Albrecht wanted to have a measure of size that would allow different types of
systems to be compared and would be independent of the technology applied. The
measure should be meaningful to the end-user or purchaser of the system, and could
be easily extracted early on in the system development cycle. It measured a system
through the analysis of functions related to the user


FPA measures the size of an application system in 2 areas: the specific user
functionality and the system characteristics.

The specific user functionality, as the name implies, is a measurement of the
functionality delivered by the application as for user request. The 5 function types
identified are external input, external output, external enquiries, internal logical files
and external interface files. For each function identified under one of the above 5
function types, the function is further classified as simple, average or complex and a
weight is given to each. The sum of the weights quantifies the size of information
processing and it is referred as the Unadjusted Function Points.

Function Point = (User Functionality) X (System Characteristics)

The general functionality of the systems will be affected by some system
characteristics. Fourteen general applications attributes are identified to rate the
general functionality of the system. A degree of influence (DI) ranges from zero to
five, from no influence to strong influence, is determined for each of the general
applications attributes. The sum of all these DIs will in turn determine a Value
Adjustment Factor for the whole projects.

The product of the Unadjusted Function Point and Value Adjustment Factor gives the
size of the application expressed in term of Adjusted Function Point.

Adjusted Function Point
= (Unadjusted Function Point) X (Value Adjustment Factor)

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