Building the Data Warehouse

Скачать в pdf «Building the Data Warehouse»

!□ □ □ пЗ

□ □□ □ ппп □ □ П°ПППп 3 □ паЗ

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.

Скачать в pdf «Building the Data Warehouse»