My first Publication Agile-Data-Warehouse-Design-eBook | Page 31

10
Chapter 1
The
7Ws
Framework
The 7Ws are
interrogatives:
question forming
words
Who is involved?
What did they do? To what is it done?
When did it happen?
Where did it take place?
HoW many or much was recorded – how can it be measured?
Why did it happen?
HoW did it happen – in what manner?
The 7Ws are an extension of the 5 or 6Ws that are often cited as the checklist in
essay writing and investigative journalism for getting the ‘full’ story. Each W is an
interrogative: a word or phrase used to make questions. The 7Ws are especially
useful for data warehouse data modeling because they focus the design on BI
activity: asking questions.
Fact tables represent verbs (they record business process activity). The facts they
contain and the dimensions that surround them are nouns, each classifiable as
one of the 7Ws. 6Ws: who, what, when, where, why, and how represent dimension
types. The 7th W: how many, represents facts. BEAM✲ data stories use the 7Ws
to discover these important verb and noun combinations.
Star schemas
usually contain
8-20 dimensions
Star schemas
support agile,
incremental BI
Detailed dimensional models usually contain more than 6 dimensions because any
of the 6Ws can appear multiple times. For example, an order fulfillment process
could be modeled with 3 who dimensions: CUSTOMER, EMPLOYEE, and
CARRIER, and 2 when dimensions: ORDER DATE and DELIVERY DATE.
Having said that, most dimensional models do not have many more than 10 or 12
dimensions. Even the most complex business events rarely have 20 dimensions.
The deep benefit of process-oriented dimensional modeling is that it naturally
breaks data warehouse scope, design and development into manageable chunks
consisting of just the individual business processes that need to be measured next.
Modeling each business process as a separate star schema supports incremental
design, development and usage. Agile dimensional modelers and BI stakeholders
can concentrate on one business process at a time to fully understand how it
should be measured. Agile development teams can build and incrementally deliver
individual star schemas earlier than monolithic designs. Agile BI users can gain
early value by analyzing these business processes initially in isolation and then
grow into more valuable, sophisticated cross-process analysis. Why develop ten
stars when one or two can be delivered far sooner with less investment ‘at risk’?
Dimensional modeling provides a well-defined unit of delivery—the star schema
—which supports the agile principles: “Satisfy the customer through early and
continuous delivery of valuable software.” and “Deliver working software fre-
quently, from a couple of weeks to a couple of months, with a preference to the
shorter time scale.”