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Data Warehouse Design

Oracle Tips by Burleson Consulting

The Data Warehouse Development Life Cycle

Oracle Data Warehouse Design

Introducing Redundancy Into An Entity/Relation Model

In Figure 4.2, a boundary line lies within a range between the size of a redundant data item and the frequency of update of the data item. The size of the data item relates to the disk costs associated with storing the item, and the frequency of update is associated with the cost of keeping the redundant data current, whether by replication techniques or by two-phase commit updates. Because the relative costs are different for each hardware configuration and for each application, this boundary may be quite different depending on the type of application. The rapid decrease in the disk storage costs designates that the size boundary is only important for very large-scale redundancy. A large, frequently changing item (for example, street_address) is not a good candidate for redundancy. But large static items (for example, service_history) or small, frequently changing items (for example, item_price) are acceptable for redundancy. Small static items (for example, gender) represent ideal candidates for redundant duplication. Because most Oracle data warehouse designs are static in the sense that data is seldom modified after it is loaded, the only consideration in the introduction of redundancy is the disk storage costs of the redundant item.

This is an excerpt from "High Performance Data Warehousing", copyright 1997.
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