A Function Point (FP) is a unit of measurement to express the amount of business functionality, an information system (as a product) provides to a user. FPs measure software size. They are widely accepted as an industry standard for functional sizing.

For sizing software based on FP, several recognized standards and/or public specifications have come into existence. As of 2013, these are −

ISO Standards

• COSMIC − ISO/IEC 19761:2011 Software engineering. A functional size measurement method.

• FiSMA − ISO/IEC 29881:2008 - Software and systems engineering - FiSMA 1.1 functional size measurement method.

• IFPUG − ISO/IEC 20926:2009 Software and systems engineering - Software measurement - IFPUG functional size measurement method.

• Mark-II − ISO/IEC 20968:2002 Software engineering - Ml II Function Point Analysis - Counting Practices Manual.

• NESMA − ISO/IEC 24570:2005 Software engineering - NESMA function size measurement method version 2.1 - Definitions and counting guidelines for the application of Function Point Analysis.

Function Point Analysis (FPA) technique quantifies the functions contained within software in terms that are meaningful to the software users. FPs consider the number of functions being developed based on the requirements specification.

Function Points (FP) Counting is governed by a standard set of rules, processes and guidelines as defined by the International Function Point Users Group (IFPUG). These are published in Counting Practices Manual (CPM).

Elementary Process (EP)

Elementary Process is the smallest unit of functional user requirement that −

• Is meaningful to the user.

• Constitutes a complete transaction.

• Is self-contained and leaves the business of the application being counted in a consistent state.

Functions:-

There are two types of functions −

• Data Functions

• Transaction Functions

Data Functions:-

There are two types of data functions −

• Internal Logical Files

• External Interface Files

Data Functions are made up of internal and external resources that affect the system.

Internal Logical Files

Internal Logical File (ILF) is a user identifiable group of logically related data or control information that resides entirely within the application boundary. The primary intent of an ILF is to hold data maintained through one or more elementary processes of the application being counted. An ILF has the inherent meaning that it is internally maintained, it has some logical structure and it is stored in a file.

External Interface Files

External Interface File (EIF) is a user identifiable group of logically related data or control information that is used by the application for reference purposes only. The data resides entirely outside the application boundary and is maintained in an ILF by another application. An EIF has the inherent meaning that it is externally maintained, an interface has to be developed to get the data from the file.