The authors characterize the notion of heterogeneous databases as the inevitable consequence of replacing the traditional data processing practice with modern database management. They articulate the current problems and future issues connected with the great proliferation and overwhelming use of heterogeneous databases and their DBMS (database management systems). They survey available DBMS solutions to these problems and issues. The limitations and advantages of various DBMS solutions are examined. To this end, a taxonomy of DBMS solutions to the problems and issues of heterogeneous databases is presented. Some of the current research and proposals on the heterogeneous-database solutions are discussed in the context of the taxonomy. >