Function Points as a Sizing Metric Function points are a synthetic method, much the same as square feet or meters, that permit the calculation of a relative size for individual software projects, applications, or subsystems even in their early requirements stages. Function point counting is typically performed when a developer wants to size and estimate development time and effort for an application or a project. In addition to functional size, other risk and complexity factors must be considered when estimating effort. When the impact of selected risk and complexity factors is considered, the effort required for development or maintenance of a certain range of function points can be estimated accurately. The Function Point Counting Process When identifying function points for a specific application, you must identify logical user data groups maintained within that application.
External inputs add, populate, revise, update, or change the data stored in the data groups.
The user data groups are processed separately within an application to permit the extraction of data and the generation of external outputs or external inquiries. An ILF is counted once per application. Their complexities are based upon their record element types and data fields. Data is often extracted from ILFs in other applications to be used in processing in the application being counted. Just as with ILFs, EIF complexities are based upon the record element types and data fields utilized.