My first Publication Agile-Data-Warehouse-Design-eBook | Page 258

238
Chapter 8
How Many
Durations
Milestone
timestamps can be
used in pairs to
create duration
facts. These should
be named by
modeling them with
stakeholders
The multiple when details of an evolving event can be used dimensionally like any
other details (for grouping and filtering), but they can also be used in pairs to
calculate the elapsed time between milestones. Some of these durations will be key
measures of process performance. It’s not always obvious which ones are signifi-
cant or what they should be called by looking at the raw when details. You find out
by using timelines to modelstorm the durations with stakeholders. You should also
discover the appropriate unit of time measurement (day, hour, or minute), and the
acceptable minimum and maximum intervals between events that can be used as
alert thresholds to drive conditional reporting applications.
Identifying and naming the right duration measures enables stakeholders to
efficiently analyze process bottlenecks.
Additional Process Performance Measures
Quantities from
different milestones
can be combined to
create process
performance
measures
Just as the multiple when details of a newly modeled evolving event can be used to
create interesting durations, other quantity details from the separate discrete events
can be combined to create additional process performance measures. For example,
you could use ORDER REVENUE, COST AT SHIPPING, and DELIVERY COST
to calculate MARGIN. You should model these additional derived measures with
stakeholders to capture their formulas and business names, and add them to the
event table with examples.
Event Timelines
Use event timelines
to visually model
milestones and
durations
The best way to discover the important milestone when details and duration
measures of an evolving event is to use an event timeline—like Figure 8-6. You
should draw a timeline showing each of the milestone dates of an evolving event in
chronological order, so that you can examine each milestone pairing visually, and
ask stakeholders for business names for the intervals between them. The most
important intervals are likely to have pre-existing names—a sure sign that they
have business value and should be modeled as facts—but new and significant
intervals can quickly be discovered and named in this way too.
You should try to get a name for each significant duration but when you have
several milestone dates, you can end up with a lot of potential durations—too
many to name in some cases. The number of durations is equal to: (Number of
timestamps x (Number of timestamps – 1) / 2 ). So if an evolving event has six
milestones, you have 6 x 5 / 2 = 15 possible durations.
Start by modeling
the fixed points on
the timeline: the
initial when detail
and any target dates
Typically, the most interesting durations will be those measured from the initial
event date (Order Date) or from a target date (Delivery Due Date). Start by adding
these fixed points on the timeline. These are the fixed value (FV) dimensions of the
evolving event. With these in place use the white space on the timeline to prompt
stakeholders for the other milestones events and their chronology.