Overview
ISO/IEC 14143-1:2007 defines the fundamental concepts of Functional Size Measurement (FSM). The standard shifts sizing focus from implementation details to the functions required by users, enabling size measurement early in the lifecycle and across the software lifetime. It establishes terminology and high-level requirements so that different FSM Methods can be compared and evaluated for conformance.
The document is intended for professionals involved in acquisition, development, maintenance, support and audit of software. It does not prescribe a specific measurement algorithm or rules for using results, but provides the conceptual basis for assessing whether a sizing method qualifies as an FSM Method.
Key Topics
- Core definitions: Functional Size, Functional Size Measurement (FSM), Functional User Requirements (FUR), Base Functional Component (BFC), BFC Type, boundary, Functional Domain, Scope of the FSM.
- Purpose of FSM: Measure software size in terms of user-required functions rather than lines of code or implementation effort.
- Characteristics of an FSM Method:
- Based on a user-perspective representation of Functional User Requirements.
- Applicable as soon as Functional User Requirements are defined.
- Derives Functional Size by assessing Base Functional Components.
- Should be independent of development methods, technology and physical components.
- BFC and BFC Types: A BFC expresses only Functional User Requirements and is classified into a single BFC Type (examples include inputs, outputs, logical transactions, and logical data stores).
- Requirements for an FSM Method:
- Define BFC attributes and assessment rules.
- Specify units for Functional Size (for example, Function Points as an illustrative unit).
- Describe applicable Functional Domain(s) and intended uses.
- State convertibility to other sizing measures where applicable.
- Process to apply an FSM Method (high-level):
- Determine the Scope of the FSM.
- Identify Functional User Requirements in scope.
- Identify and classify BFCs.
- Assign numeric values to BFCs and calculate Functional Size.
Applications
ISO/IEC 14143-1:2007 is valuable for:
- Early sizing during requirements and acquisition phases.
- Portfolio sizing and benchmarking across projects.
- Cost estimation and vendor selection when combined with productivity metrics.
- Audits and conformance checks of candidate FSM Methods.
- Supporting consistent communication between stakeholders about software functional size.
Related Standards
This part is the conceptual foundation of the ISO/IEC 14143 series. Related parts include:
For organizations seeking consistent, technology-independent functional sizing, ISO/IEC 14143-1:2007 provides the essential concepts and structure to evaluate and apply FSM methods reliably.
Open preview (PDF)Information technology — Software measurement — Functional size measurement — Part 1: Definition of concepts
