In recent years, research on distributing databases over networks has become increasingly important. In this paper, we concentrate on the issues of the interoperability of heterogeneous DBMSs and enforcing integrity across a multi-database made in this fashion. This has been done through a cooperative project between Aberdeen and Linko/spl uml/ping universities, with database modules distributed between the sites. In the process, we have shown the advantage of using DBMSs based on variants of the functional data model (FDM), which has made it remarkably straightforward to interoperate queries and schema definitions. Further, we have used the constraint transformation facilities of P/FDM (Prolog implementation of FDM) to compile global constraints into active rules installed locally on one or more AMOS (Active Mediators Object System) servers. We present the theory behind this, and the conditions for it to improve performance.