In this method, the number and type of functions supported by the software are utilized to find FPC(function point count). The steps in function point analysis are:

• Count the number of functions of each proposed type.

• Compute the Unadjusted Function Points(UFP).

• Find Total Degree of Influence(TDI).

• Compute Value Adjustment Factor(VAF).

• Find the Function Point Count(FPC).

The explanation of above points given below:

Count the number of functions of each proposed type:

Find the number of functions belonging to the following types:

• External Inputs: Functions related to data entering the system.

• External outputs: Functions related to data exiting the system.

• External Inquiries: They leads to data retrieval from system but don’t change the system.

• Internal Files: Logical files maintained within the system. Log files are not included here.

• External interface Files: These are logical files for other applications which are used by our system.

Compute the Unadjusted Function Points(UFP): Categorise each of the five function types as simple, average or complex based on their complexity. Multiply count of each function type with its weighting factor and find the weighted sum. The weighting factors for each type based on their complexity are as follows:

• Find Total Degree of Influence: Use the ’14 general characteristics’ of a system to find the degree of influence of each of them. The sum of all 14 degrees of influences will give the TDI. The range of TDI is 0 to 70. The 14 general characteristics are: Data Communications, Distributed Data Processing, Performance, Heavily Used Configuration, Transaction Rate, On-Line Data Entry, End-user Efficiency, Online Update, Complex Processing Reusability, Installation Ease, Operational Ease, Multiple Sites and Facilitate Change. Each of above characteristics is evaluated on a scale of 0-5.

• Compute Value Adjustment Factor(VAF): Use the following formula to calculate VAF VAF = (TDI * 0.01) + 0.65

• Find the Function Point Count: Use the following formula to calculate FPC FPC = UFP * VAF

Advantages of the Functional Point Method:

• In pre-project stage the estimates can be prepared.

• Based on requirement specification documents the method’s reliability is relatively high.

Disadvantages of Functional Point Method:

• It is not good for real time systems and embedded systems.

• Many cost estimation models like COCOMO uses LOC and hence FPC must be converted to LOC.