Building the Data Warehouse

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■■ The industry track record of success strongly suggests it.

■■ The end user is unable to articulate requirements until the first iteration is done.

■■ Management will not make a full commitment until actual results are tangible and obvious.

■ Visible results must be seen quickly.

What may not be obvious is the role of the data model in iterative development. To understand the role of the data model during this type of development, consider the typical iterative development suggested by Figure 3.22. First, one development effort is undertaken, then another, and so forth. The data warehouse serves as a roadmap for each of the development efforts, as seen in Figure 3.23.

When the second development effort ensues, the developer is confident that he or she will intersect his or her effort with the first development effort because all development efforts are being driven from the data model. Each succeeding development effort builds on the preceding one. The result is that the different development efforts are done under a unifying data model. And because they are built under a single data model, the individual iterative efforts produce a cohesive and tightly orchestrated whole, as seen in Figure 3.24.

When the different iterations of development are done with no unifying data model, there is much overlap of effort and much separate, disjoint development. Figure 3.25 suggests this cacophonous result.

There is, then, an indirect, yet important, correlation between the data model and the ability to achieve long-term integration and a harmonious effort in the incremental and iterative development of a data warehouse.

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