Database Reference
In-Depth Information
You can, however, solve this problem programmatically by using validation code that will verify the values
match at the level of days. In Figure
4-14
you can see an example of this.
Figure 4-14.
Comparing dates between tables
We discuss ETL programming further in Chapter 6, but for now let's move on to an example of how a date
dimension table can be used in multiple ways.
Role-Playing Dimensions
Role-playing dimension tables are used repeatedly for slightly different purposes or, well, roles. So, the term
role-playing
comes from the fact that the same table plays many roles. The classic example of a role-playing
dimension is a time dimension that links to a fact table multiple times. Figure
4-15
shows an example that can be
found in Microsoft's
AdventureWorks2008DW
demonstration database.
This may seem to be too simplistic an explanation, but this is really all there is to it. It is possible to have role-
playing dimensions that do not involve dates. An example might be geographic regions. But dates are by far the
most common example.
