Proposition d'un noyau et d'une structure pour les modèles de tâches orientés utilisateurs

User task analysis is a critical step in the design process of interactive systems. The large set of user task models available today may lead to assume that this step is well supported. These models, which possess sometimes an associated tool, expose a wide spectrum of proficiency such as evaluation, interrogation, or simulation. Temptation to use them jointly presume interworkings. But, even at the syntactic level it remains impossible. Furthermore, following various work, problems appear as well on task's caracteristic, as documentation or coherency. To try to remedy, a modular approach is proposed to structure these models and answer these requirements. Thus, we will expose here our central module, the core, which contains minimal datas to describe the activity and this, independently of any idea of specialization.