From the Formal Specifications of Users Tasks to the Automatic Generation of the HeI Specifications Adel Mahfoudhit, Mourad Abed+ & Dimitri Tabary+ t Department of Computer Science, Science Faculty of Sfax, Rte So ukra km 3.5, BP: 802-3018 Sfax, Tunisia Tel: +2164274390 Fax: +2164274437 Email: adel.mahfoudhi@fss.mu.tn :j: lAMIH (UMR CNRS 8530), Universite de Valenciennes, BP: 311-59304, Valenciennes Cedex 9, France Tel: +3332751 14 66 Fax: +3342751 13 16 Email: {mourad.abed.dimitri.tabary}@univ-valenciennes.fr This paper presents an approach to the construction of a task model of a method, named TOaD (Task Object Oriented Design), used for the development of an interactive system. This approach is based on a formal notation, which gives quantitative results which may be checked by designers and which provide the possibility of performing mathematical verifications on the models. The modelling formalism is based on the joint use of the object approach and high level Petri nets. The concepts borrowed from the object approach make it possible to describe the static aspects of tasks and the Petri nets enable the description of dynamics and behaviour. We also describe a software aid tool for the manipulation of these models, which allows the editing and the simulation of a task model. In order to facilitate the comprehension of the method, an extremely simple example of the air traffic control will be given. Keywords: task analysis, HeI specification, complexity evaluation, formal method, object approach, Petri nets. A. Blandford et al. (eds.), People and Computers XV - Interaction without Frontiers © Springer-Verlag London Limited 2001