Technical report TR95-16. A large-scale interoperable database system operating in a dynamic environment should provide a uniform access user interface to its components, scalability to larger networks, evolution of database schema and apllications, composability of client and server components, and preserve component autonomy. To address the research issues presented by such systems, we introduce the Distributed Interoperable Object Model (DIOM). DIOM promotes an adaptive approach to interoperation and mediation, aimed at improviing the robustness and scalability of the interoperation services used for integrating and accessing heterogeneous information resources. DIOM's main features include the explicit representation of semantics in data sources through the DIOM base interfaces, the use of interface composition mechanisms to support the incremental design and construction compound interoperation interfaces, the decoupling of semantic heterogeneity from the representational mismatch, the deferment of semantic conflict resolution to the query submission time instead of at the time of information gathering and integration, and a clean interface between distributed interoperable component objects that supports the independent evolution and management of such objects. To make DIOM concrete, we outline the Diorama architecture, which includes important auxiliary services such as domain-specific library functions, object linking databases, and query decomposition and packaging strategies. Several practical examples and application scenarios illustrate the usefulness of DIOM.