My first Publication Agile-Data-Warehouse-Design-eBook | Page 69

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Chapter 2
If you find yourself generalizing several details you should ask questions about how
similar the event stories really are. If stories have very different details you will
probably want to model them in separate event tables, because highly generalized
events rapidly become meaningless to stakeholders.
Figure 2-9
Adding where
details
Check that each
where is a detail of
“who does what” not
just who or what
When you ask for additional where details emphasize that you are looking for
locations that are specific to the whole event, not the existing who or what details.
This helps avoid (for the moment) detail about detail — like customer address and
product manufacturing address — that are not dependent on the event. These
reference addresses will be modeled as dimensional attributes of CUSTOMER and
PRODUCT once the event is complete (see Chapter 3).
Each time you finish collecting a W-type, it’s good practice to quickly scan
through the previous Ws to check for missing details. After you finish asking
where questions check to see if any of the where details remind the stakeholders
of additional whos, whats and whens.
Modelstorming with Whiteboards
Whiteboards are the agile practitioner’s favorite collaborative modeling tool. They
are ideal tools for modelstorming snippets of your design at a time but even the
most generous whiteboards can be challenged by the width of a full BEAM✲
table. Here’s some practical advice for using them and other tools for event
modeling:
Use “whiteboard on a roll” plastic sheets to extend/replace your finite white-
board. Large post-it™ notes or flipchart paper and masking tape work too
but are not so neat or forgiving for iterative design. Sheets with a 2.5cm grid
work very well for event tables.