Datasheet

Part I: The Data Warehouse: Home for Your Data Assets

To determine the size you need for your data warehouse, follow these steps:

1. Determine the mission, or the business objectives, of the data

warehouse.

Ask the question, “Why bother creating this warehouse?”

2. Determine the functionality that you want the data warehouse to

have.

Figure out what types of questions users will ask.

3. Determine what contents (types of data) the data warehouse needs to

support its functionality.

Understand what types of answers your users will seek.

4. Determine, based on the content volume (which is based on the

functionality, which in turn is based on the mission), how big you

need to make your data warehouse.

Realizing That a Data Warehouse

(Usually) Has a Historical Perspective

In almost all situations, a data warehouse has a historical perspective.

Some amount of time lag occurs between the time something happens in

one of the data sources (a new record is added or an existing one is

modified in a corporate application, for example) and the time that the

event’s results are available in the data warehouse.

The reason for the time lag is that you usually bulk-load data into a

data warehouse in large batches. Figure 1-2 illustrates a model of bulk-

loading data.

Bulk-loading is giving way to messaging, the process of sending a small number

of updates (perhaps only one at a time) much more frequently from the data

source to a target — in this case, the data warehouse. With messaging, you

have a much more up-to-date picture of your data warehouse’s subject areas

than you do with bulk-loading because you’re putting information into an

operational data store (as discussed in Chapter 20), rather than into a tradi-

tional data warehouse. Additionally, the world of service-oriented architec-

tures (SOAs) and Web 2.0 are driving the messaging and presentation of data

to near real-time in some industries. The combination of the data warehouse’s

historic perspective with this near-real-time sourcing of information enables

business leaders to monitor the situation and make decisions at the speed of

the business.

05_407479-ch01.indd 2005_407479-ch01.indd 20 1/26/09 7:23:41 PM1/26/09 7:23:41 PM