Computer Communications, Special Issue on FDTs Use Case Maps and Lotos for the Prototyping and Validation of a Mobile Group Call System p. 1 Use Case Maps and LOTOS for the Prototyping and Validation of a Mobile Group Call System Daniel Amyot and Luigi Logrippo School of Information Technology and Engineering (SITE) 150 Louis-Pasteur, University of Ottawa, Ontario, Canada, K1N 6N5 +1 613 562 5800 (ext. 6704) damyot@site.uottawa.ca, luigi@eiti.uottawa.ca ABSTRACT — SPEC-VALUE, a rigorous scenario-driven approach for the description and validation of complex sys- tem functionalities at the early stages of design, is presented. It is based on two notations. The first notation, called Use Case Maps (UCMs), is used to capture functional requirements. UCMs can help reasoning about system-wide functionalities at a high level of abstraction before a prototype is generated. The second notation is the formal specifi- cation language LOTOS. UCM scenarios are translated into LOTOS specifications, which animate UCMs with the help of tools. LOTOS-based techniques, especially specification-level testing, can be used to validate designs. It is shown how SPEC-VALUE can help to produce better-quality designs and standards and to improve human understanding with reduced time and costs. A real-life case study is provided: the Group Call service of the mobile data system General Packet Radio Services (GPRS). KEY WORDS: Causal Scenarios, LOTOS, Telecommunications Standards, Use Case Maps, Validation Testing. 1. INTRODUCTION 1.1 The Design and Standardization Challenges Numerous industries and standardization bodies (ITU, ISO, ANSI, ETSI, TIA, etc.) are con- stantly at work to design new telecommunications products and new standards for such products, involving increasingly complex functionalities. These services require increasingly complex archi- tectures and protocols. In the early stages of many conventional design processes used in industry and in standardization bodies, many features, services, and functionalities are described using informal operational descriptions, tables and visual notations such as Message Sequence Charts (MSCs) [26]. As these descriptions evolve, they quickly become error-prone and difficult to man- age. The need of precisely documenting all stages of the design process, which is very important in the industrial environment, becomes critical in the standardization process, where there is inter- national scrutiny for which the stages are formalized and must undergo formal review and approval [3]. The following issues should be addressed: