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# 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