Avi Silberschatz

Providing Multidatabase Access

One of the major tasks in the design of a multidatabase system (MDBS) is the definition and maintenance of the global schema. Traditionally, this is accomplished by requiring the local databases participating in the MDBS to provide “export schemas” that are merged into a global schema. Resolution of schema and data incompatibilities, and mapping between local and global schemas are, in general, very difficult tasks that must be performed at the multidatabase level. We believe that a solution to this formidable problem may lie in the shifting of responsibility for these tasks to the local level. We propose a model in which the MDBS administrator defines the global schema as a view that is to be maintained by each of the participating databases. The MDBS layer supports submission and processing of (global) queries expressed over a union of such views. Each participating database must provide a view of its database that conforms to the global specification and must promise to respond to queries formulated over this view. We discuss the architecture of such systems and the problems involved in the processing of global queries.