function point
A metric that quantifies how much business functionality an information system delivers, used to determine the functional size of a software system.
Key Points
- Technology-agnostic sizing based on what users can do with the system.
- Counts typical elements such as external inputs, external outputs, external inquiries, internal logical files, and external interface files.
- Supports effort estimation, productivity benchmarking, scope control, and vendor contracting.
- Can be calculated early from requirements and refined as details emerge (e.g., IFPUG or COSMIC methods).
Example
A project team scoping a new banking app identifies features like create account (input), view balance (output), transaction search (inquiry), customer data (internal file), and credit-bureau interface (external file). They tally the function points to estimate effort and compare vendor proposals.
PMP Example Question
Which metric should a project manager use to size the scope from business requirements in a technology-independent way to support effort estimates for a new payroll system?
- Story points
- Function points
- Lines of code
- Velocity
Correct Answer: B — Function points
Explanation: Function points measure user-visible functionality independent of technology, enabling functional size estimation. Story points and velocity are team-specific agile measures, and lines of code depend on the chosen technology.
