Building the Data Warehouse

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There are a number of serious and uncompromising limitations to the scenario of the direct access of data in the data warehouse. Some of these are as follows:

■■ The request must be a casual one in terms of response time. It may take as long as 24 hours for it to be satisfied. This means that the operational processing that requires the data warehouse data is decidedly not of an online nature.

■■ The request for data must be for a minimal amount of data. The data being transferred is measured in terms of bytes, not megabytes or gigabytes.

■■ The technology managing the data warehouse must be compatible with the technology managing the operational environment in terms of capacity, protocol, and so on.

■ The formatting of data after it is retrieved from the data warehouse in preparation for transport to the operational environment must be nonexistent (or minimal).

Figure 3.46 A direct query against the data warehouse from the legacy applications environment.

These conditions preclude most data ever being directly transferred from the data warehouse to the operational environment. It is easy to see why there is a minimal amount of backward flow of data in the case of direct access.

Indirect Access of Data Warehouse Data

Because of the severe and uncompromising conditions of transfer, direct access of data warehouse data by the operational environment is a rare occurrence. Indirect access of data warehouse data is another matter entirely. Indeed, one of the most effective uses of the data warehouse is the indirect access of data warehouse data by the operational environment. Some examples of indirect access of data warehouse data follow.

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