The function point (FP) method calculates an estimate using the parameters of inputs, outputs, inquiries, and files. The technique was introduced by Albrecht in 1979 to measure the size of data processing systems from the end user’s point of view to determine an estimated development effort. FP's advantage is that estimators can calculate effort when a defined use case or in-depth system analysis is not available. Estimators calculate function points by summing the number of internal logical files, external interface files, external inputs, external inquiries, and external outputs. Function points are numerical values that measure software size determined from data processing types rather than from software development complexity.
The FP method is appropriate to estimate size and cost but cannot estimate effort. Function points represent the amount of functionality released to the user by determining the data transactions, and operations that involve data crossing the boundaries of the application. The FP method provides an estimation method that allows managers to project software size early in the project life cycle. It is independent of the technology used in the development of the software project.