Building the Data Warehouse

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The primary data is the nonkey data that relates directly to the key of the record. As an example, suppose the key identifies the sale of a product. The element of time describes when the sale was finalized. The primary data describes what product was sold at what price, conditions of the sale, location of the sale, and who were the representative parties.


The secondary data—if it exists—identifies other extraneous information captured at the moment when the snapshot record was created. An example of secondary data that relates to a sale is incidental information about the product being sold (such as how much is in stock at the moment of sale). Other secondary information might be the prevailing interest rate for a bank’s preferred customers at the moment of sale. Any incidental information can be added to a data warehouse record, if it appears at a later time that the information can be used for DSS processing. Note that the incidental information added to the snapshot may or may not be a foreign key. A foreign key is an attribute found in a table that is a reference to the key value of another table where there is a business relationship between the data found in the two tables.


Once the secondary information is added to the snapshot, a relationship between the primary and secondary information can be inferred, as shown in Figure 3.35. The snapshot implies that there is a relationship between secondary and primary data. Nothing other than the existence of the relationship is implied, and the relationship is implied only as of the instant of the snapshot. Nevertheless, by the juxtaposition of secondary and primary data in a snapshot record, at the instant the snapshot was taken, there is an inferred relationship of data. Sometimes this inferred relationship is called an “artifact.” The snapshot record that has been described is the most general and most widely found case of a record in a data warehouse.

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