Building the Data Warehouse

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Jan 1

AAA — Alaska Alt AAG — German Air AAR — Ark Electric BAE — Brit Eng

Figure 3.36 A snapshot is taken of a reference table in its entirety every six months—one approach to the management of reference tables in the data warehouse.

Jan 1

AAA — Amber Auto AAT — Allison’s AAZ — AutoZone BAE — Brit Eng

Jan 1    — add TWQ — Taiwan Dairy

Jan 16 — delete AAT Feb 3 — add AAG — German Power Feb 27 — change GYY — German Govt

A complete snapshot is taken on the first of the year.

Figure 3.37 Another approach to the

Changes to the reference table are collected throughout the year and are able to be used to reconstruct the table at any moment in time.

management of reference data.

Cyclicity of Data—The Wrinkle of Time

One of the intriguing issues of data warehouse design is the cyclicity of data, or the length of time a change of data in the operational environment takes to be reflected in the data warehouse. Consider the data in Figure 3.38.

The current information is shown for Judy Jones. The data warehouse contains the historical information about Judy. Now suppose Judy changes addresses. Figure 3.39 shows that as soon as that change is discovered, it is reflected in the operational environment as quickly as possible.

Once the data is reflected in the operational environment, the changes need to be moved to the data warehouse. Figure 3.40 shows that the data warehouse has a correction to the ending date of the most current record and a new record has been inserted reflecting the change.

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