Building the Data Warehouse

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The key structure of operational data may or may not contain some element of time, such as year, month, day, and so on. The key structure of the data warehouse always contains some element of time. The embedding of the element of time can take many forms, such as a time stamp on every record, a time stamp for a whole database, and so forth.

The Structure of the Data Warehouse

Figure 2.5 shows that there are different levels of detail in the data warehouse. There is an older level of detail (usually on alternate, bulk storage), a current level of detail, a level of lightly summarized data (the data mart level), and a level of highly summarized data. Data flows into the data warehouse from the operational environment. Usually significant transformation of data occurs at the passage from the operational level to the data warehouse level.

Once the data ages, it passes from current detail to older detail. As the data is summarized, it passes from current detail to lightly summarized data, then from lightly summarized data to highly summarized data.

monthly sales by product line 1981-1992

Figure 2.5 The structure of the data warehouse.

Subject Orientation

The data warehouse is oriented to the major subject areas of the corporation that have been defined in the high-level corporate data model. Typical subject areas include the following:

■■ Customer ■■ Product

■■ Transaction or activity ■■ Policy

■    Claim

■    Account

Each major subject area is physically implemented as a series of related tables in the data warehouse. A subject area may consist of 10, 100, or even more

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