Building the Data Warehouse

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J Jones 19 92—present ■ 123 Main Credit — AA


change the ending date


J Jones 1993-present Rte 4, Austin, TX Credit — AA

Figure 3.40 The activities that occur in the data warehouse as a result of the change of address.


data warehouse

^__ ____>

“wrinkle of time”

4^ ___


24-hour delay



Figure 3.41 There needs to be at least a 24-hour lag—a “wrinkle of time»—between the time a change is known to the operational environment and the time when the change is reflected into the data warehouse.

A more powerful reason for the wrinkle of time is that it imposes a certain discipline on the environments. With a 24-hour wrinkle there is no temptation to do operational processing in the data warehouse and data warehouse processing in the operational environment. But if the wrinkle of time is reduced—say, to 4 hours—there is the temptation to do such processing, and that is patently a mistake.

Another benefit of the wrinkle of time is opportunity for data to settle before it is moved to the data warehouse. Adjustments can be made in the operational environment before the data is sent to the data warehouse. If data is quickly sent to the warehouse and then it is discovered that adjustments must be made, those adjustments need to be made in both the operational environment and the data warehouse environment.

Complexity of Transformation and Integration

At first glance, when data is moved from the legacy environment to the data warehouse environment, it appears that nothing more is going on than simple extraction of data from one place to the next. Because of the deceptive simplicity, many organizations start to build their data warehouses manually. The programmer looks at the movement of data from the old operational environment to the new data warehouse environment and declares “I can do that!” With pencil and coding pad in hand, the programmer anxiously jumps into the creation of code within the first three minutes of the design and development of the data warehouse.

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