Building the Data Warehouse

Скачать в pdf «Building the Data Warehouse»

When data is organized around the subject-in this case, the customer—each key has an element of time, as shown in Figure 2.9.

customer ID

customer ID

from data to date

customer ID

from date to date name address phone dob sex



credit rating





number of transactions average tx amount tx high tx low

txs cancelled

customer ID

activity date

customer ID



activity date

amount location for item invoice no clerk ID order no

order no line item no sales amount invoice no deliver to

Figure 2.9 Each table in the data warehouse has an element of time as a part of the key structure, usually the lower part.

Some tables are organized on a from-date-to-date basis. This is called a continuous organization of data. Other tables are organized on a cumulative monthly basis, and others on an individual date of record or activity basis. But all records have some form of date attached to the key, usually the lower part of the key.

Day 1-Day n Phenomenon

Data warehouses are not built all at once. Instead, they are designed and populated a step at a time, and as such are evolutionary, not revolutionary. The costs of building a data warehouse all at once, the resources required, and the disruption to the environment all dictate that the data warehouse be built in an orderly iterative, step-at-a-time fashion. The “big bang” approach to data warehouse development is simply an invitation to disaster and is never an appropriate alternative.

Скачать в pdf «Building the Data Warehouse»