Building the Data Warehouse

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ISSUE: After the data model has been built, the system of record is identified. The system of record normally resides in the operational environment. The system of record represents the best source of existing data in support of the data model. The issues of integration are very much a factor in defining the system of record.

9. Has the frequency of extract processing—from the operational system of record to the data warehouse environment—been identified? How will the extract processing identify changes to the operational data from the last time an extract process was run?

■    By looking at time-stamped data?

■    By changing operational application code?

■    By looking at a log file? An audit file?

■    By looking at a delta file?

■    By rubbing “before” and “after” images together?

ISSUE: The frequency of extract processing is an issue because of the resources required in refreshment, the complexity of refreshment processing, and the need to refresh data on a timely basis. The usefulness of data warehouse data is often related to how often the data warehouse data is refreshed.

One of the most complex issues—from a technical perspective—is determining what data is to be scanned for extract processing. In some cases, the operational data that needs to pass from one environment to the next is

straightforward. In other cases, it is not clear at all just what data should be examined as a candidate for populating the data warehouse environment.

10.    What volume of data will normally be contained in the DSS environment?

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