Databases Reference
In-Depth Information
The results of these queries can be used to determine which elements would
be useful for reporting and analytical purposes. If the data element has never
been populated, then this does not need further study. If a data element has
not been changed in years, this may indicate core reference data that is still
valid or it may indicate that this data is no longer being captured and/or
maintained by the operational system. Obsolete data elements do not need to
be addressed in the modeling process.
It is also helpful to have business analysts participate in this analysis. They
can often help the team to understand the data content. Over time, the original
name and meaning of a column can be lost or changed. It is helpful to know
how the data is used today. The objective is not to isolate data elements that
have been requested for reporting, but to identify all data elements that contain
business data. This is often done through an elimination process. For example,
data elements that are obsolete or those that are used to drive security for
the operational system do not contain business data that would need to be
included in the data warehouse.
Data profiling
is a more comprehensive set of activities intended to look at
data across all systems, operational and analytical. This is described in more
detail in Chapter 8.
TIP
Look at all the data elements, not just those specifically identified for
reporting.
After there is a clear understanding of what the business is trying to
accomplish and a familiarity with the data that is available, it is time to look at
how that data should be organized.
What Is a Dimensional Model?
A
dimensional model
is a data model organized for the purpose of user under-
standability and high performance. There are two basic parts of a dimensional
model: the
dimensions
and the
facts
. These are the building blocks that comprise
all dimensional models, simple or complex.
Dimensions
Dimensions are groupings of data elements in major business categories.
Common dimensions include the following:
Customers
Products
Dates
