There is a great deal of confusion over the meaning of data warehousing. Simply defined, a data warehouse is a place for data, whereas data warehousing describes the process of defining, populating, and using a data warehouse. Creating, populating, and querying a data warehouse typically carries an extremely high price tag, but the return on investment can be substantial. Over 95% of the Fortune 1000 have a data warehouse initiative underway in some form.
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phase of ETL, if it is performed at all. Data warehouses can be designed to store data at the detail level (each individual transaction), at some aggregate level (summary data), or a combination of both. The advantage of summarized data is that typical queries against the warehouse run faster. The disadvantage is that information, which may be needed to answer a query, is lost during aggregation. The tradeoff must be carefully weighed, because the decision can not be undone without rebuilding and