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Data warehouses are typically made up of multiple star schemas, called data marts. A star schema, with a central Fact table and four dimension tables. Queries on star schemas usually restrict columns in the dimension tables to retrieve rows from the central fact table. Star Schemas were first devised by Red Brick Systems to speed up queries on data loaded from operational databases at intervals of about a day, with no updates between loads. Variant designs (allowing some updates) were adopted by Oracle, DB2, Sybase IQ and recently Vertica.
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