From User Requirements to Conceptual Design in Data Warehouse Design - Data Warehousing Design and Advanced Engineering Applications - page 11

Figure 2. A basic fact schema for the SALES fact

collected, during the requirement analysis phase,
to allow effective multidimensional modelling in
the next phase.

concepts modelled are facts, measures, dimen-
sions, and hierarchies. In the following we intui-
tively define these concepts, referring the reader
to Figure 2 that depicts a simple fact schema for
modelling invoices at line granularity; a formal
definition of the same concepts can be found in
(Golfarelli, 2008).
A fact is a focus of interest for the decision-
making process; typically, it models a set of events
occurring in the enterprise world. A fact is graphi-
cally represented by a box with two sections, one for
the fact name and one for the measures. Examples
of facts in the trade domain are sales, shipments,
purchases; in the financial domain: stock exchange
transactions, contracts for insurance policies. It is
essential for a fact to have some dynamic aspects,
i.e., to evolve somehow across time. The concepts
represented in the data source by frequently-updated
archives are good candidates for facts; those rep-
resented by almost-static archives are not. As a
matter of fact, very few things are completely static;
even the relationship between cities and regions
might change, if some borders were revised. Thus,
the choice of facts should be based either on the
average periodicity of changes, or on the specific
interests of analysis.
A measure is a numerical property of a fact,
and describes one of its quantitative aspects of

The Dimensional Fact Model

The DFM is a graphical conceptual model, spe-
cifically devised for multidimensional design,
aimed at:

• effectively supporting conceptual design;

• providing an environment in which user

queries can be intuitively expressed;
supporting the dialogue between the de- •

signer and the end-users to refine the speci-
fication of requirements;
creating a stable platform to ground logical •

design;
providing an expressive and non-ambigu- •

ous design documentation.

DFM was first proposed in 1998 by Golfarelli and
Rizzi and continuously enriched and refined during
the following years in order to optimally suit the va-
riety of modeling situations that may be encountered
in real projects of small to large complexity.
The representation of reality built using the
DFM consists of a set of fact schemata. The basic