Building the Data Warehouse

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Fig 2.30 The data warehouse sits at the center of a large framework.

Purging Warehouse Data

Data does not just eternally pour into a data warehouse. It has its own life cycle within the warehouse as well. At some point in time, data is purged from the warehouse. The issue of purging data is one of the fundamental design issues that must not escape the data warehouse designer.

In some senses, data is not purged from the warehouse at all. It is simply rolled up to higher levels of summary. There are several ways in which data is purged or the detail of data is transformed, including the following: ■■ Data is added to a rolling summary file where detail is lost.

■■ Data is transferred to a bulk storage medium from a high-performance medium such as DASD.

■■ Data is actually purged from the system.

■■ Data is transferred from one level of the architecture to another, such as from the operational level to the data warehouse level.

There are, then, a variety of ways in which data is purged or otherwise transformed inside the data warehouse environment. The life cycle of data—including its purge or final archival dissemination—should be an active part of the design process for the data warehouse.

Reporting and the Architected Environment

It is a temptation to say that once the data warehouse has been constructed all reporting and informational processing will be done from there. That is simply not the case. There is a legitimate class of report processing that rightfully belongs in the domain of operational systems. Figure 2.31 shows where the different styles of processing should be located.

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