The contribution of the requirements engineering in the success of projects is incontestable and it has been proved, through studies and statistics that succeed or fail a project depends generally on requirements engineering. This domain became the centre of interest of a big number of researchers to present the most adequate model and process to succeed the requirements engineering and so succeed the project. Requirements engineering is done according to a process spread all along the life cycle of the system and that aims to provide methods, technologies and tools allow developing and implanting some computing systems providing the services and the information expected by their users, demanded by their acquirers, and compatible with their functioning environment. Requirements engineering process is executed on three principals steps: First, the requirements elicitation to identify future system needs .Then, the specification and the requirements documentation validated or modified following a discussion between the different actors of the process. The end product which is an outfit of models that allows to take into account the actors’ point of view, represent not only the final specifications but also the intermediate results. This permits having coherent and well structured documents. The validation and verification of the requirement specification is the final step. On this article, after a presentation of principal challenges that requirements engineering face and notably in specification step, we will define the fundamental notion of a role that will allow us to surround a system in all his perspectives : the organizational, the functional and even the intentional, etc. Then, after a study of some models of requirements engineering we will propose a model of process of requirements engineering with focusing on role notation and its participation in the different process steps.