Query Decomposition, Optimization and Processing in Multidatabase Systems.
Cem Evrendilek, Asuman Doğaç · 1995
1. Introduction One way of achieving interoperability among heterogeneous, federated DBMSs is through a multidatabase system that supports a single common data model and a single global query language on top of different types of existing systems. The global schema of a multidatabase system is the result of a schema integration of the schemas exported from the underlying databases, i.e., local databases. A global query language is used by users of the multidatabase system to specify queries against the global schema. Three steps are necessary to process the global queries [MY 95]: First a global query is decomposed into subqueries such that the data needed by each subquery are available from one local database. Next each subquery is translated to a query or queries of the corresponding local database system and sent to a local database system for execution. Third the results returned by the subqueries are combined into the answer. Multidatabase query optimization has been addressed in...