We describe the design of Mariposa, an experimental distributed data management system that provides high performance in an environment of high data mobility and heterogeneous host capabilities. The Mariposa design unifies the approaches taken by distributed file systems and distributed databases. In addition, Mariposa provides a general, flexible platform for the development of new algorithms for distributed query optimization, storage management, and scalable data storage structures. This flexibility is primarily due to a unique rule-based design that permits autonomous, local-knowledge decisions to be made regarding data placement, query execution location, and storage management.>