TITLE: ``Query Reformulation in Multidatabase Systems using Semantic Knowledge''

ABSTRACT:

We consider a multidatabase system (MDBMS) with a common object-oriented model, based on the ODMG standard, and local databases that may be relational, object-oriented, or file systems. The MDBMS interface could be different from the union of the local interfaces, and may include views of particular local databases, integrity constraints, and knowledge about data replication in local databases. Query reformulation is made difficult by the variety of semantic knowledge that is used to describe the MDBMS, and the complexity of the Object Query Language. We present a reformulation algorithm which exploits semantic knowledge, (represented as integrity assertions and mapping rules), for semantic rewriting based on pattern-matching. It is general enough to re-use the results of previously computed queries in the MDBMS.

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