Database administrators (DBAs) have always said that having non-normalized or de-normalized data is bad. Why is de-normalized data now okay when its used for Decision Support?
A. Normalization of a relational database for transaction processing avoids processing anomalies and results in the most efficient use of database storage. A data warehouse for Decision Support is not intended to achieve these same goals. For Data-driven Decision Support, the main concern is to provide information to the user as fast as possible. Because of this, storing data in a de-normalized fashion, including storing redundant data and pre-summarizing data, provides the best retrieval results. Also, data warehouse data is usually static so anomalies will not occur from operations like add, delete and update of a record or field.
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