AbstractThis paper introduces an approach to software development in which a series of working implemen- tations are generated automatically from a series of formal specifications. The implementations are data stores, communicating through standard protocols. The specifications are precise object models, in which operations are described in terms of pre- and post-conditions. The approach is evolutionary, in the sense that the specification may evolve while the system is in use, in response to changes in requirements, and any changes to the specification are automatically reflected in the structure of the implementation, and in the representation of any data currently stored.