In this paper, we design and implement a prototypical heterogeneous distributed database system, named DHIM (Distributed Heterogeneous Information Management). The objectives of DHIM are two-fold: one is to realize the global update synchronization mechanism which preserve the global serializability of concurrent executions and the local site autonomy in tightly coupled heterogeneous distributed database systems, and the other is to implement an open architectural distributed database system. The open architecture implies that DHIM is able to operate independently from the features of element local database systems. Therefore, any database system can be federated into DHIM as an element database system.