Many problems encountered in providing enterprise-wide information are related to the integration of databases and systems that have been independently developed and also to the management of changes and transformations of data from one database (or system) into another. A major requirement is to accommodate heterogeneity and at the same time to preserve the autonomy of the components. This paper presents our approach to a repository-driven federated system based on a propagation mechanism. The Stuttgart Information and Exploration System (SIES), is characterized by its main components: the Federation Manager, the Propagation Manager and the Re-pository System.