Functional point analysis - A software estimation technique

Functional point is a standard unit of measure that represents functional size of a software application. Functional point analysis quantifies the functionality of a software application from user perspective based on a logical design. It’s technology independent and consistent across the project and across the organization.

There are five standard functions divided into two categories in functional point analysis as named below.

1. Data Function: There are two type of data functions - Internal logical file (ILF) & External interface file (EIF)

a. Internal logical file (ILF) – ILF is a group of data which are logical and user identifiable. Data defined by ILF is maintained through the elementary process occurring within the boundary of application whose functions are being counted.

b. External interface file (EIF) – EIF is also a group of data which are logical and user identifiable just like ILF. Here, the difference is EIF data is maintained outside the boundary of application whose functions are being counted. Based on the count of data element type (DET) and record element type (RET), low, average and high complexity is assigned to a data function - ILF or EIF and based on complexity of an ILF or EIF, function points are assigned to it as per below table.

c. Data element type (DET) – DET is a user recognizable and non-repeatable data of a data function – ILF or EIF.

d. Record element type (RET) – RET is user identifiable subgroup of DETs and it is part or subset of a data function - ILF or EIF.

Data Functions (ILF, EIF)
RETs	DETs				Functional Point
	1-19	20-50	51-51+		Complexity	ILF FP	EIF FP
1	L	L	A		L	7	5
1-5	L	A	H		A	10	7
6-6+	A	H	H		H	15	10

2. Transaction Function There are 3 types of transaction functions - External input (EI),External output (EO) & External inquiry (EQ).

a. External input (EI) – EI is a data entered by the user or data/file fed by an external application.

b. External output (EO) – EO is a report created by the application in consideration where the report contains derived information/data.

c. External inquiry (EQ) – EQ is a report created by the application in consideration where the report doesn’t contain the derived info/data. Based on the count of data element type (DET) and file transaction reference (FTR), low, average and high complexity is assigned to a transaction function - EI, EO or EQ and based on complexity of an EI, EO or EQ, function points are assigned to it as per below table.

d. File Transaction reference (FTR) – A FTR is an either ILF or EIF referenced by the transaction function of the application whose functions are being counted.

Transaction Functions (ILF, EIF)
FTR(EI)	DTE				FTR(EO, EQ)	DET
	1-4	5-15	16+			1-5	6-19	20+
0-1	L	L	A		0-1	L	L	A
2	L	A	H		2-3	L	A	H
2+	A	H	H		3+	A	H	H
Functional Points
Complexity			EO FP		EQ FP		EI FP
L			4		3		3
A			5		4		4
H			7		6		6

Count of data functions and transaction functions will give the total unadjusted function point count which can be put as in below table

Sl No.	File/Trans Name	Function Type(Data/Trans.)	Fn Type Name (ILF,EIF,EI,EO,EQ)	DET	RET	FTR	Complexity	Function Point
Total Unadjusted Function Point

There are also some other factors which influence the functional size of a software application. It's called value adjustment factor as a group. There are 14 parameters in the value adjustment factor known as general system characteristics listed as in below table.

General System Characteristics(GSC)	Weight(0-5)
Data Communication
Distributed data processing
Performance
Heavily Used Configuration
Transaction Rate
Online data entry
End user efficiency
Online update
Complex processing
Reusability
Installation ease
Operational ease
Multiple sites
Facilitate change
Total Degree of Influence
Variable Adjustment Factor

These characteristics are given weight value of 0-5. Value adjustment factor is calculated as VAF = (TDI * 0.01) + 0.65

And, final function point count of a software application is derived as UFPC*VAF where UFPC is unadjusted function point count and VAF is value adjustment factor.