Improving the quality of a system begins by their requirements elicitation: the challenge is to bridge the gap between the requirements of the client and their formal specification defined by the scientist. A first step consists on understanding and rewriting the existing requirements. Along the development process, we introduce formal terms in the requirements coming the formal specification and make explicit the interactions between them by a glossary. The trace of the requirements and their corresponding specification is managed and serves to simplify the activities of validation and verification. The validation is studied since the understanding of the first requirements and all along the development of their formal specification. The verification may detect imperfections like incoherences and ambiguities in both the formal specification and their corresponding requirements.