1. Introduction
Everybody agrees on the fact that elaboration of any information system is a difficult task. Many reasons are incriminated : organisations are perpetually changing, collecting future end users real needs is not easy... In a classical process, information systems design concerns two types of actors : (1) the end-user, professionnal of the domain ; he/she is consulted for the analysis of the system, and will get a ready-to-use product, (2) the computer scientist elaborates the product ; helped with interviews and questionnaires, he collects end-users needs, makes a synthesis of the gathered information, and then defines and develops the product. The end-user thus has two opposite positions : he is both the provider (of information) and the client (of final product). This