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Query Rewriting
Query Rewriting is a technique used in mediation based data integration systems for translating the queries formulated over the mediated schema to a query over the various sources by making use of the view definitions. Mediation based data integration system hides from the end user the underlying heterogeneity of the various data providing sources linked to it by providing a uniform query interface in the form of a mediated schema. This schema is also referred to as the global schema whereas the schema of the various data sources is collectively referred to as the local schema. The local schema and the mediated schema are mapped to each other using view definitions. The queries formulated on the mediated schema cannot be directly used to query the sources. Therefore query rewriting translates such a query formulated over the global schema to a query over the various data sources. Examples include bucket algorithm, Minicon algorithm, inverse rules algorithm.〔 This rewritten query is then evaluated to obtain the query response making use of the data obtained by querying the data sources.
==See also==
* Data integration
* Schema Matching
* Data Virtualization
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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