Building the Data Warehouse

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■    All purely operational data needs to be eliminated.


■    Referential integrity relationships need to be turned into artifacts.


■    Derived data that is frequently needed is added to the design.


The structure of the data needs to be altered when appropriate for the following:


■    Adding arrays of data


■    Adding data redundantly


■    Further separating data under the right conditions


■    Merging tables when appropriate


existing


systems


environment




design the data warehouse



existing


systems


environment




extract


integrate


change time basis of data condense data efficiently scan data


Figure 9.2 Migration to the architected environment.


Stability analysis of the data needs to be done. In stability analysis, data whose content has a propensity for change is isolated from data whose content is very stable. For example, a bank account balance usually changes its content very frequently-as much as three or four times a day. But a customer address changes very slowly-every three or four years or so. Because of the very disparate stability of bank account balance and customer address, these elements of data need to be separated into different physical constructs.


The data warehouse, once designed, is organized by subject area. Typical subject areas are as follows:


■■ Customer ■■ Product ■■ Sale ■■ Account


■    Activity


■    Shipment


Within the subject area there will be many separate tables, each of which is connected by a common key. All the customer tables will have CUSTOMER as a key, for example.

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