Critical issues in multidatabase systems

For many applications. a multidataha.<;e approach constitutes an attractive a1t.emative to a single, integrated data.ba.o;e. In lhis paper we describe our experiences gained in Ute COUlf:.e of the development of experimental muHidataba.sesystems: OMNIBASE, at the University of Houston and InlerBase at Purdue University. We concentrate on the problems of query processing and multidalabase transaction management and discuss solutions that were developed within both projects. We identify the main issues related to supporting updAtes spanning across multiple autonomous database~ and define an extended transaction model suitable for heterogeneous complltinK environments. Then we review the major olllstanding reseaxch problems and discll!>S the directions of further research in the area of multidatabase systems.