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An Introduction to FPA

This document aims to introduce Function Point Analysis (FPA), a technique for measuring the size of a system from a user's point of view.

FPA is 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 measures a system through the analysis of functions related to the user. It is also a vehicle to estimate cost and resources required for software development and maintenance.

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 low, average or high 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.

Besides, the general functionality of the system will be affected by the following general system characteristics:


A degree of influence (DI) ranges from zero to five, from no influence to strong influence, is determined for each of the general system characteristics. The sum of all these DIs will in turn determine a Value Adjustment Factor for the whole project.

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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