A function point is a unit of measurement to express the amount of
business functionality an information system (as a product) provides
to a user. The cost (in dollars or hours) of a single unit is
calculated from past projects
May be an example helps:
- past: in the last 300 workingdays peter finished implementing features with a calculated total of 600 functionpoints.
- from the past on average peter implemented 2 functionpoints per day.
- presence: There is a new software feature X to be implemented that has 100 functionpoints.
Assuming that peter still has the same development velocity you can predict that the new feature will riquire 200 days.
Why using functionpoints?
calulating function point is much easier than estemaiting effort to implement a feature.
If a manager knows how to calulate the functionpoints and he knows from the past that
- susan can do 5 functionpoints per day
- peter can do 2 functionpoints per day
The manager can estimate how long it will take to implement the project and decide if peter or susan should do the job.