Today's enterprise computing needs require the interoperability of heterogeneous information sources. This warrants complex architectures with weak central control involving structured, semi-structured or unstructured data. Functionality similar to that of database management systems are also required, e.g., support for queries. This paper presents our approach based on ad-hoc federations using a mediation system of active meta objects. Our framework adheres to established and emerging industrial standards, e.g. XML, CORBA, MOF. We also combine sound transaction processing and agent system concepts for coordinating and controlling component interaction. Our approach is feasible based on the results of a prototyping effort.