My first Publication Agile-Data-Warehouse-Design-eBook | Page 71

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Chapter 2
For more structured modeling sessions with larger groups of stakeholders
you might want to use a data projector and model directly into a projected
spreadsheet. If so, investigate the use of short throw, interactive projectors
and annotation software. With these tools, modelstormers can huddle round
a projected interactive whiteboard without casting shadows — but don’t let
gadgets get in the way of modeling.
If you are using the BEAM✲Modelstormer spreadsheet you will find that the
primary details (the subject, object, and initial when detail) of each table are
frozen, so that you can scroll horizontally without losing the context of each
event story. This spreadsheet also draws a pivoted ER table diagram in sync
with the BEAM✲ table, so you can see a list of all the details at any time.
Appendix C provides recommendations for tools and further reading that will
improve your collaborative modeling efforts.
How Many?
Ask “how many?”
to discover facts,
measures, KPIs
How many questions are used to discover the quantities associated with an event
that will become facts in the physical data warehouse and the measures and key
performance indicators (KPIs) on BI reports and dashboards. Again, you repeat
the main clause of the event as a question to the stakeholders, but this time with
“how many” and its variants: “how much”, “how long” etc. inserted to make
grammatical sense. For example:
CUSTOMER orders how many PRODUCTs?
How much are PRODUCT orders worth?
In both cases you want the name of the quantity. Likely answers to these ques-
tions — ORDER QUANTITY and REVENUE — have been added to the event table
in Figure 2-10 along with examples that show a wide range of values. You should
ask how much/many questions for each detail to see if it has any interesting quanti-
ties that should be associated with the event. So you could ask:
How many CUSTOMERs order PRODUCTs?
The stakeholders would probably like to answer “thousands” but for each order
event story it is always one customer. For details like this where the answer is
always one, or zero if the detail is missing (not mandatory), there isn’t a useful
additional quantity to name and add to the event. When you have checked all the
details for quantities, you should follow up with the general question:
How else would you measure this event?