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Chapter 4
Conformed
dimensions are
shared by
multiple
fact tables
Swappable, rollup
and role-playing
dimensions are
conformed at the
dimensional
attribute level
The simplest technical definition of a conformed dimension is a single physical
dimension table shared by multiple fact tables or exact replicated copies of a master
dimension, if fact tables are distributed on multiple database servers. Separate
distinct dimensions can also be conformed at the attribute level if they contain
conformed attributes with identical business meanings and identical contents that
line up as common report row headers. Three types of dimension are conformed at
the attribute level, they are:
Swappable dimensions [SD] that are subsets of conformed dimensions. For
example, a CUSTOMER dimension (1M people) and a subset EXTENDED
WARRANTY CUSTOMER dimension (100K people) are conformed if they
describe the same customer in exactly the same way. These two dimensions
would allow product sales and extended warranty claims to be compared for all
customers or just warranty holding customers. Swappable dimensions are cov-
ered in Chapter 6.
Rollup dimensions [RU] with conformed attributes in common with their base
dimensions. Figure 4-3 shows an example of the conformed when dimensions
CALENDAR and MONTH. These two dimensions can be used to compare
daily and monthly granularity measures at the Month, Quarter, or Year level.
Rollup dimensions are typically used to describe planning events and aggregate
fact tables.
Role-playing dimensions [RP]: Single physical dimensions used to play multi-
ple logical roles. For example, a CALENDAR [RP] dimension used to play the
role of ORDER DATE and PAYMENT DATE.
Figure 4-3
When dimensions,
conformed at the
attribute level