Utilizing Functional Size Measurement Methods for Real Time Software Systems Cigdem Gencel cgencel@ii.metu.edu.tr Onur Demirors demirors@ii.metu.edu.tr Erhan Yuceer Erhany@AYESAS.com Abstract There are various approaches developed for software size measurement. After Albrecht developed his original method which is based on quantifying functionality delivered to the users in 1979, variations of Functional Size Measurement (FSM) methods have been developed and become widely used. Among those, IFPUG FPA, Mk II FPA, COSMIC FFP and NESMA FSM have become international ISO standards being conformant to ISO/IEC 14143. This paper presents the results obtained by applying Mk II FPA and COSMIC FFP to two real-time software systems which have control as well as algorithmic components. The evaluation of these methods with respect to their measurement processes and the difficulties faced during the measurement process are also discussed. 1. Introduction Reliable size measurement of software systems is still one of the significant challenges of software engineering. Until today, various approaches for sizing software have been developed. The metrics and methods based on “functionality” have become widely-used after originally introduced by Albrecht in 1979 [1], [2]. After that, variants of the method have been developed. During the 1980s and 1990s, several authors have suggested new FP counting techniques that intended to improve the original FPA or extend its field of application [3]. In 1996, the International Standards Organization (ISO) started to work on Functional Size Measurement (FSM) to establish common principles of those methods and published ISO/IEC 14143-1 standard on FSM [4]. Detailed descriptions of four methods; Mk II FPA [5], IFPUG FPA [6], COSMIC FFP [7] and NESMA FSM [8] are recently published as international standards that are certified by ISO. There are a number of studies on the evaluation and comparison of the FSM methods in the literature. Rule discusses the similarities and differences between IFPUG FPA and Mk II FPA in his study [9]. In [10], Lother and Dumke evaluated FSM methods with respect to their suitability for certain functional domains and their maturity, and discussed the issues of FSM. In another study [11], three estimation methods applied early in the life cycle to a case project, are compared. In [12], Rollo discusses the issues associated with sizing web applications and evaluated IFPUG FPA, Mk II FPA and COSMIC FFP. Mk II FPA and COSMIC FFP methods are compared and the differences between them are discussed in another study [13]. In this paper we presented the results obtained by applying Mk II FPA and COSMIC FFP to two development projects of real-time applications. First application is one of the subsystems of an avionics management system for small to medium size commercial aircrafts. The other one is Collision Avoidance System (CAS) component of a Traffic Alert and Collision Avoidance System. Among other methods which are applicable to measure the size of real-time software such as Feature Points [14], 3-D Function Points [15], Analytical Software Size Estimation Technique-Real-Time [16] and Full Function Points (FFP) [17], we selected Mk II FPA and COSMIC FFP methods for being international ISO standards and having detailed measurement manuals, which are required in order to make reliable measurement. The descriptions of the projects, the application of Mk II FPA and COSMIC FFP to these projects and the results obtained are presented in the second section. Last section discusses the results of this study, the difficulties faced during the measurement process, and the evaluations of the methods. 2. Application of the Methods to Projects Both projects are developed by the same organization, which is a SW-CMM Level 3 company. Project-1 is a development project of one of the subsystems of an avionics managements system for small to medium size commercial aircrafts on a Flight Display System. It is developed according to RTCA/DO-178B Software Considerations in Airborne Systems and Equipment Certification and will be certified by Federal Aviation Administration. The software complies with DO-257A, ‘Minimum Operational Performance Standards for the Depiction of Navigation Information on Electronic Maps’ as a basis