William wishes to thank Mike Cross (mcross@racenter.com), data warehouse director at Rent-A-Center, for his contributions to this month's column.
The one overriding constant about data warehousing is that the data warehouse will change. Data designs that you spend months perfecting will become obsolete overnight, and unforeseen business requirements will require a different view of the data. If you want to be a successful data warehouse architect, you can either become very astute at accommodating change or you can design for the unknown.
数据挖掘研究院 Figure 1: Simplified Daily Income Table One of the problems with this design is that if additional income categories appear, as they inevitably will, you will need to add them to the table structure. After several iterations of adding, renaming and subtracting, the table transforms itself into a very inefficient structure. Other problems with this design are that developers need to understand the history of all changes to use it effectively, and you will need to include all income columns for every store, even if it does not apply to that store. An abstract design for this same structure would look like Figure 2. 数据挖掘研究院  Figure 2: Abstract Design Daily Income Table This structure, combined with the lookup table, which is shown in Figure 3, allows for new income categories without changing the existing structure and provides the added benefit of defining categories and showing relationships between categories. 数据挖掘研究院
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