Building the Data Warehouse

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There is, however, a downside to profiling records in the data warehouse. Whenever the use of the profile technique is contemplated, note that a certain capability or functionality of the data warehouse is lost. Of necessity, detail is lost whenever aggregation is done. Keep in mind, however, that losing detail is not necessarily a bad thing. The designer of the profile record needs to ensure that the lost detail is not important to the DSS analyst who will ultimately be using the data warehouse. The data architect’s first line of defense (and easily the most effective one) is to ensure that such detail is not terribly important is to build the profile records iteratively. By doing so, the data architect has the maneuverability to make changes gracefully. The first iteration of the design of the contents of the profile record suggests the second iteration of design, and so forth. As long as the iterations of data warehouse development are small and fast, there is little danger the end user will find many important requirements left out of the profile record. The danger comes when profile records are created and the first iteration of development is large. In this case, the data architect probably will paint himself or herself into a nasty corner because important detail will have been omitted.


A second approach (which can be used in conjunction with the iterative approach) to ensure that important detail is not permanently lost is to create an alternative level of historical detail along with the profile record, as shown in Figure 3.44. The alternative detail is not designed to be used frequently; it is stored on slow, inexpensive, sequential storage and is difficult to get to and awkward to work with. But the detail is there should it be needed. When management states that they must have a certain detail, however arcane, it can always be retrieved, albeit at a cost of time and money.

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