My first Publication Agile-Data-Warehouse-Design-eBook | Page 260

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Chapter 8
How Many
DF
: Derived Fact, calculated from other columns in the same table.
DTn : Date/Time, numbered in chronological order for use in duration formulas.
All the durations within an event should be defined using the same unit of meas-
ure; for example, all [days] or all [hours]. This avoids errors when durations are
compared or used in calculations.
Using Timelines for Documentation
Timelines should be
used to permanently
document duration
definitions within the
model
Timelines are part of
the definition of an
accumulating
snapshot. They also
make great training
material for BI users
Although the DF formulas in the column types of Figure 8-7 are useful for ETL
and BI developers, the best way to document the meaning of each duration for the
wider audience is to use an event timeline. The timelines you create in a model-
storming workshop should also become a permanent part of the model documen-
tation, along with the other BEAM ✲ artifacts: event tables, dimension tables,
hierarchy charts, and the event matrix.
Timelines are to evolving events as hierarchy charts are to dimensions. Dimension
tables need hierarchy charts to document the levels of their conformed hierarchies.
Accumulating snapshots need timelines to document their event sequences and
durations. Just as you can use relative spacing on a hierarchy chart to show relative
aggregation, spacing on a timeline can show the relative durations of stages within
a process, and highlight the most time-consuming events that must be carefully
monitored. Timelines are an essential part of the training material for stakeholders
who need to work with complex evolving events.
Timelines can be added to the footers or summaries of reports, as simple static
graphics, to explain the meaning of the duration figures they contain.
Using Timelines for Business Intelligence
Use dynamic
timelines for
data visualization
on reports and
dashboards
Timelines are not only useful for modeling and documenting event sequences, they
make great tools for visualizing process flow in BI applications too. Dynamic or
animated versions of the timelines you model can be used on reports and dash-
boards to display live status counts and durations. In Figure 8-8, an example
dashboard for monitoring CUSTOMER ORDERS shows the average durations
between milestone events and the number of order items at each stage.
BI developers can create dynamic timelines within reports by displaying duration
measures as horizontal stacked bar charts.
The Back of the Napkin, Dan Roam (Portfolio, 2008) Chapter 12, “When can we fix
things” contains some great ideas on drawing timelines to solve when problems.
Other chapters describe how to draw pictures to solve other 7Ws (who, what,
where, how many, why and how) related business problems.