Function Point Analysis

Function Point Analysis was developed by Allen Albrecht. It is a methodology used to estimate the amount of "functionality" software performs in terms of data input, generated output, and file maintenance and utilization (Albrecht 83). Function points are derived from a measurement of the software's information domain and its processing complexity. The information domain is classified into five user identifiable function types, each of which has three levels of complexity. The five types and their associated complexity levels are described in the following sections. More detailed information about the User Function Types is included in theCOSMOS Technical Reference (see Function Point Complexity Assignments). COSMOS follows the counting practices as documented in the International Function Point User's Group (IFPUG) Counting Practices Manual, Version 4.0 for New Development Projects.

User Identifiable Function Types

1. Number of External Inputs

External input (EI)is a transactional function that processes data or control information from outside the boundary of the application under consideration. An external input adds, modifies, or deletes information from internal logical files (described below). The external input is unique if either the input format or the processing logic is unique.

Complexity	Description
Low	Few data elements included in the external input type and a limited number of internal logical file types referenced by the external input type
Average	The external input type not conclusively low or high
High	Many data elements included in the external input type and a significant number of internal logical file types referenced by the external input type

2. Number of External Outputs

External output (EO)is a transactional function that generates data or control information to be sent outside the boundary of the application under consideration. The external output is unique if either the output format or the processing logic is unique. Output can be files, reports, or messages sent to users or to other applications.

Complexity	Description
Low	A single column or two columns with no subtotals
Average	Multiple columns with subtotals
High	Multiple file references and complicated data transformations

3. Number of Internal Logical Files

A set of logically related data maintained inside the application.

Complexity	Description
Low	Few record types
Average	The internal logical file type not conclusively low or high
High	Many record types

4. Number of External Interface Files

A set of logically related data used inside the application, but maintained external to the application.

Complexity	Description
Low	Few record types
Average	The external file type not conclusively low or high
High	Many record types