Building the Data Warehouse

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Next, on the one-year horizon, estimate the maximum and minimum number of rows in the table. This estimate is the one that is the most problematic for the designer. If the table is for customers, use today’s estimate, factoring in business conditions and the corporate business plan. If there is no existing business


Estimating rows/space for the warehouse environment


1.    For each known table:


How big is a row (in bytes)


-biggest estimate -smallest estimate For the 1-year horizon


What is the maximum number of rows possible?


What are the minimum number of rows possible?


For the 5-year horizon


What is the maximum number of rows possible?


What is the minimum number of rows possible?


For each key of the table What is the size of the key (in bytes)


Total maximum 1-year space = biggest row x 1-year max rows Total minimum 1-year space = smallest row x 1-year min rows plus index space


2.    Repeat (1) for all known tables.


Figure 4.1 Space/row calculations.


today, estimate the total market multiplied by the expected market share. If the market share is unpredictable, use an estimate of what a competitor has achieved. In short, start with a reasonable estimate of customers gathered from one or more sources.


If the warehouse is to contain information about activity, go from the estimated number of customers to the estimated activity per unit of time. Again, the same logic is used: looking at current business profiles, a competitor’s profile, economic projections, and so forth.

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