Building the Data Warehouse

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The overflow environment can be held in a single medium, such as magnetic tape, which is cheap for storage and expensive for access. It is entirely possible to store a small part of the archival level of data online, when there is a probability that the data might be needed. For example, a bank might store the most recent 30 days of activities online. The last 30 days is archival data, but it is still online. At the end of the 30-day period, the data is sent to magnetic tape, and space is made available for the next 30 days’ worth of archival data.


Now consider another example of data in an architected environment in the banking/financial environment. Figure 4.8 shows customer records spread across the environment. In the operational environment is shown current-value data whose content is accurate as of the moment of usage. The data that exists at the light level of summarization is the same data (in terms of definition of data) but is taken as a snapshot once a month.


Where the customer data is kept over a long span of time—for the past 10 years-a continuous file is created from the monthly files. In such a fashion the history of a customer can be tracked over a lengthy period of time.


Now let’s move to another industry—manufacturing. In the architected environment shown in Figure 4.9, at the operational level is the record of


dual levels of granularity in the banking environment


operational





60 days worth of activity

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