Functional Size of Real-Time Software: Overview of Field Tests

In most software cost estimation models, software size is the key cost driver. Such models use either a technical measure of software size, based on lines of code, or alternatively a functional size measure which can be known earlier in the software life cycle. However, even though Function Points is the most widely used functional size measure in the MIS domain, practitioners have often pointed out its limitations for measuring the size of real-time or embedded software; therefore, it is not currently considered as an adequate input parameter for estimating real-time software effort. In 1997, a new extension to Function Points (referred to as Full Function Points – FFP) was introduced for measuring the functional size of real-time software in order to address the most obvious weaknesses of IFPUG’s Function Points while retaining compatibility with traditional Function Points for MIS software. Full Function Points was also recently accepted as a new measurement standard for real-time software by the International Software Benchmarking Standards Group. This paper reports on the key concepts of this extension, as well as on the preliminary results of the measurement field tests carried out in different organizations. The ability of FFP to adequately capture the functional size of real-time software is illustrated by FFP and FPA measurements taken on the same software products. Preliminary results, using additional collected data, to support exploratory analysis of the unit effort and schedule delivery date based on FFP are also presented. 1. CONTEXT Measures can be used to quantify software products as well as the process by which they are developed. Once these measures are obtained, they can be used to build cost estimation models and productivity models [1], for instance. In this perspective, a key measure is the size of a software product. There are basically two kinds of size measures: technical measures and functional measures. On the one hand, technical size measures are used to quantify software products and processes from a developer’s point of view. These can be used in efficiency analysis to improve the performance of the design, for instance. On the other hand, functional measures are used to quantify software products and services from a user’s perspective. Being independent of technical development and implementation decisions, functional measures can therefore be used to compare the productivity of different techniques and technologies. In this context, major organizations frequently use functional size measurement methods to quantify the software products included in their outsourcing contracts. Function Points Analysis (FPA), first introduced in 1979 by Allan Albrecht of IBM [2], is an 1 Serge Oligny and Alain Abran are respectively Director – Technological innovations and Director of UQAM Software Engineering Management Research Laboratory in Montréal (http://www.info.uqam.ca/Labo_Recherche/lrgl.html) , they can be reached at [email protected] and [email protected] 2 Jean-Marc Desharnais is Managing Partner and Principal Consultant with Software Engineering Laboratory in Applied Metrics (http://www.lmagl.qc.ca/), he can be reached at [email protected] 3 Pam Morris is Director Consulting and Training with Total Metrics (http://www.totalmetrics.com), she can be reached at [email protected]