Critical issues in multidatabase systems

For many applications, a multidatabase approach constitutes an attractive alternative to a single, integrated database. In this paper we describe our experiences gained in the course of the development of experimental multidatabase systems: OMNIBASE, at the University of Houston and InterBase at Purdue University. We concentrate on the problems of query processing and multidatabase transaction management and discuss solutions that were developed within both projects. We identify the main issues related to supporting updates spanning across multiple autonomous databases and define an extended transaction model suitable for heterogeneous computing environments. Then we review the major outstanding research problems and discuss the directions of further research in the area of multidatabase systems.