Abstract. This paper focuses on the interoperability of autonomous legacy databases with the idea of meeting the future requirements of an organization. It describes a general architecture and a methodology intended to address the probroviding new client applications with an abstract interface defined from the new requirements and the description of the legacy databases. The architecture n a hierarchy of mediators that provide the abstract interface of the new system. The methodology integrates the processes of standard database forward design, database reverse engineering and database federation. The discussion is illustrated by a small case study.