Query processing and transforming for a federated database System
During an industrial research project of the German Telekom we have designed and developed the system VHDBS, which is a federated database system for integrating information from pre-existing and legacy databases. It offers an objectoriented data model and a common query language in the SQUOQL style. In this paper we discuss the query processing and transforming for VHDBS. We show how a query against the federated database is split up into subqueries for different local databases, and how the results of the subqueries are synthesized to form the final result for the federated database. The corresponding algorithms are introduced. Moreover, we will also introduce the repository concept that serves as the basis for formulating and processing federated queries.
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