Function Points

Basic idea

Measure software size by the functionality delivered to the user, not by code volume. Counts inputs, outputs, inquiries, internal files, and external interfaces; multiplies by complexity weights; adjusts by 14 general system characteristics.

Key formulas

• Adjusted FP: $FP = UFP \times VAF$
• VAF: $VAF = 0.65 + 0.01 \sum_{i=1}^{14} F_i$, with each $F_i \in [0,5]$
• $UFP = \sum_{\text{type, complexity}} (\text{count} \times \text{weight})$

Is used to express the amount of functionality in a software system, as seen by the user. A higher number of function points indicates more functionality. Typically used to:

• Estimate the cost and effort required to design, code and test a software system.

• Predict the number of errors

• Predict the number of components

• Measure productivity

  Function Points are computed from the Software Requirements Specification (SRS)

Advantages of function points

• Measure the size of the solution instead of the size of the problem
• Requirements are the only thing needed for function points count
• Can be estimated early in analysis and design
• Is independant of technology
• Is independant of programming languages

Disadvantages of function points

• A well defined requirements specification is necessary
• Gaining proficency is not easy, the learning curve is quite long
• Could be quite time-consuming this could be costly

Siblings

• Challenges in cost estimation.
• Cocomo
• Cost Estimation
• Size Estimation
• Techniques for cost estimation
• Use case points (UCP)