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Extended Function Point (EFP) Metrics

  • Last Updated : 20 Sep, 2019

Function Point (FP) measure was inadequate for many engineering and embedded systems. To overcome this, A number of extensions to the basic function point measure have been proposed. These are as follows:

    Feature Points:

  • Feature Points are computed by counting the information domain values.
  • It can be used in those areas where there is a level of complexity, is comparatively very high.
  • Function point (FP) measure is the subset for the Feature point.
  • But both the Function point and feature point represents the functionality of the systems

Table for feature point calculation:

Sr. No.Measurement ParameterCount**Weighting factor
1Number of external inputs(EI)*4
2Number of external outputs(EO)*5
3Number of external Inquiries(EQ)*4
4Number of internal files (ILF)*7
5Number of external interfaces(EIF)*7
6Algorithms used Count total*3

3D function points:

  • Data, Functional, and control are three dimensions represented by 3D function points.
    1. Data: User interfaces and data as in the original method.
    2. Control: Real-time behavior(s)
    3. Function: Internal processing
  • Data dimension calculation is the same as the FPs. Feature-Transformation is done in the functional dimension. While in the control dimension, feature-Transition is added.
  • The 3D Function Point method was proposed by Boeing.
  • It is designed to solve two problems with the Albrecht approach.

Compute the FP, feature point and 3D-function point value for an embedded system with the following characteristics:

1. Internal data structures = 8
2. No. of user inputs = 32
3. No. of user outputs = 60
4. No. of user inquiries = 24
5. No. of external interfaces = 2
6. No. of transformation = 23
7. No. of transition = 32 

Assume complexity of the above counts is average case = 3.


Step-1: We draw the Table first for computing FPs.

Sr. No.Measurement ParameterCount**Simple Weighting factorAverage Weighting factorComplex Weighting factorCalculated Value
1Number of external inputs(EI)32*346128
2Number of external outputs(EO)60*457300
3Number of external Inquiries(EQ)24*34696
4Number of internal files (ILF)8*7101580
5Number of external interfaces(EIF)2*571014
6Number of Transformation23*23
7Number of Transition32*32
Count – Total—–>673

Step-2: Find the sum of all fi (1 to 14)

Σ(&fi) = 14 * 3 = 42 

Step-3: Calculate the functional point:

FP = Count-total * [0.65 + 0.01 *Σ(&fi) ]
= 618 * [0.65 + 0.01 * 42]
= 618 * [0.65 + 0.42]
= 618 * 1.07 
= 661.26 

Step-4: Calculate the Feature point:

= (32 *4 + 60 * 5 + 24 * 4 + 80 +14) * 1.07 + {12 * 15 *1.07} 
= 853.86 

Step-5: Calculate the 3D function point, it is calculated by counting the total calculated values. So, for 3D function points, the required index is 673.

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