Building the Data Warehouse

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In operational systems, the relationships between databases are handled by referential integrity.


But, in the data warehouse environment:


•    There is much more data than in the operational environment.


•    Once in the warehouse, the data doesn’t change.


•    There is a need to represent more than one business rule over time.


•    Data purges in the warehouse are not tightly coordinated.


Figure 3.33 Referential integrity in the data warehouse environment.


Artifacts in the data warehouse environment:


•    can be managed independently


•    are very efficient to access


•    do not require update


other data is still in the warehouse. In any case, trying to replicate referential integrity in the data warehouse environment is a patently incorrect approach.


Snapshots in the Data Warehouse


Data warehouses are built for a wide variety of applications and users, such as customer systems, marketing systems, sales systems, and quality control sys-


tems. Despite the very diverse applications and types of data warehouses, a common thread runs through all of them. Internally, each of the data warehouses centers around a structure of data called a “snapshot.” Figure 3.34 shows the basic components of a data warehouse snapshot.


Snapshots are created as a result of some event occurring. Several kinds of events can trigger a snapshot. One event is the recording of information about a discrete activity, such writing a check, placing a phone call, the receipt of a shipment, the completion of an order, or the purchase of a policy. In the case of a discrete activity, some business occurrence has occurred, and the business must make note of it. In general, discrete activities occur randomly.

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