Requirements elicitation and modelization are recognized as the most important phases of the development process. Nevertheless, the allotted time to this step is usually lower than 20% of the entire project. Furthermore, this percentage decreases in the case of model driven developments. Most researches concentrate on the development phase, and use the MDA approach. We propose extending the traditional perimeter of the model driven development process during the requirements phase. A better understanding of company and user problems is the main factor for the success in developing a well-adapted system. To improve communication between functional and technical experts, our proposition is composed of a language and a metamodel to describe the user's functional needs. Then an interpretation mechanism, using model transformations, adapts the definition of needs to the targeted profile. The main goal is to improve the quality of specifications and to give reliable and precise information to the next phases. Moreover, we seek to improve the performance of this phase using model transformations to automate an important series of mechanisms.