This paper provides a framework for understanding functional sizing as it relates to user requirements. Drawing on relevant international standards and other published material, it will explore the different types of requirements and provide the basis for identifying functional user requirements and sizing software.

In 1998, ISO1 (the International Organization for Standardization) and IEC (the International Electrotechnical Commission) jointly published the first part in a series of International Standards for Functional Size Measurement (FSM). This standard, ISO/IEC 14143-1:19982, contains provisions to which FSM Methods must conform. In particular, an FSM Method must measure “functional” requirements and must not measure “technical” or “quality” requirements. In 1999, IFPUG initiated a process to create an International Standard from the IFPUG Counting Practices Manual Release 4.1 Series (CPM)3 to be published as ISO/IEC 20926:2003. With its publication, this version of the IFPUG CPM conforms to ISO/IEC 14143-1:1998. To ensure that future versions of the CPM can be published as revisions to this International Standard, the CPM has to remain conformant to ISO/IEC 14143-14. When dealing with issues, and later when revising the CPM, it is important to remain cognizant of the differences between “functional” requirements, an “technical” or “quality” requirements. To achieve this, it is necessary to clearly define functional requirements, and be able to place them into context.

• Section 1 Introduction - Provides the overview, background and outline of the paper.

• Section 2 A Historical Perspective - Discusses the history of functional size measurement from the initial work of Allan Albrecht through to the publication of ISO/IEC 14143-1:1998. It also explains the metamorphosis of Albrecht’s concept from function point analysis to functional size measurement.

• Section 3 Other Relevant Works - Explores other relevant material, some of which is not always associated with software, to provide a stable foundation for the conclusions drawn in this paper.

• Section 4 Putting it All Together - Provides a clearer statement of what functional size measurement is and, therefore, what the CPM should be measuring by combining elements from the previous sections.

• Section 5 Recommendations for Implementation - Examines the implications for industry. Functional size measurement is narrower in scope than the function point analysis from which it evolved, and this will have some impact for many organizations.

• Section 6 Summary - Summarizes the main points of this paper.

• Section 7 Works Cited, Works Consulted - Provides a bibliography of additional references.