This chapter stressed the importance of data normalization when constructing a relational database. Why then is it important to de-normalize data in a data warehouse?
Wherever possible, normalized tables pertaining to selected events should be consolidated into de-normalized tables. Because of the vast size of a data warehouse, inefficiency caused by joining normalized data can be very detrimental to the performance of the system. A three-way join between tables in a large data warehouse may take an unacceptably long time to complete and may be unnecessary. Since historical data are static in nature, nothing is gained by constructing normalized tables with dynamic links.
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