The first step of most database design methodologies consists in eliciting part of the user requirements from various sources such as user interviews and corporate documents. These requirements formalize into a conceptual schema of the application domain, that has proved to be difficult to validate, especially since the visual representation of the ER model has shown understandability limitations from the end-users standpoint. In contrast, we claim that prototypical user interfaces can be used as a two-way channel to efficiently express, capture and validate data requirements. Considering these interfaces as a possibly populated physical view on the database to be developed, reverse engineering techniques can be applied to derive their underlying conceptual schema. We present an interactive tool-supported approach to derive data requirements from user interfaces. This approach, based on an intensive user involvement, addresses a significant subset of data requirements, especially when combined with other requirement elicitation techniques.