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This document aims to introduce the Function
Point Analysis (FPA), a technique for measuring size of a
system from an user's point of view.
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. It 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.
The general functionality
of the systems will be affected by the following general
system characteristics are identified to rate the general
functionality of the system.
| (a) |
Data Communication; |
(h) |
On-line Update; |
| (b) |
Distributed
Processing; |
(i) |
Complex Processing; |
| (c) |
Performance; |
(j) |
Reusability; |
| (d) |
Heavily Used
Configuration; |
(k) |
Installation
Ease; |
| (e) |
Transaction
Rate; |
(l) |
Operational Ease;
|
| (f) |
On-line Data
Entry; |
(m) |
Multiple
Sites; and |
| (g) |
End-User
Efficiency; |
(n) |
Ease of Change. |
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.
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Adjusted Function Point = (Unadjusted Function Point) X (Value Adjustment Factor)
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