This article describes a formal approach to specify and develop database applications. This approach consists of two complementary phases. In the first phase, B specifications are automatically generated from UML class, state and collaboration diagrams describing the data and the transactions of the system we are developing. In the second phase, these specifications are successively refined until they become close enough to a relational implementation. The tool supporting this approach is implemented as an extension of the Rational Rose tool to develop and visualize graphical (UML) and formal (B) notations in a single environment.