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Chapter 3
Figure 3-10a, b, c
Hierarchy charts for
Time and Product
Levels can be
spaced evenly or
relative to the
aggregation they
provide
Hierarchy charts
can show single or
multiple hierarchies
When you draw a hierarchy chart you can space out the level tics evenly, as in
Figure 3-10a and 3-10c, or in rough approximation of their relative aggregation, as
in Figure 3-10b where levels that expose more details are placed further below their
parent than levels that reveal fewer details. Relative spacing gives stakeholders a
visual clue as to how much more detail they can expect to drill down to at each
level, or how selective filters would be placed at various levels. You can also anno-
tate levels with their approximate cardinalities, as in Figure 3-10a. Large gaps or
jumps in cardinality on a hierarchy chart can prompt stakeholders for missing
levels that would give them ‘finer grain’ drill-down and even more interesting
descriptions.
In addition to providing a visual comparison of levels within a single hierarchy, a
hierarchy chart can also be used to compare multiple hierarchies for a single
dimension, as in Figure 3-10b, or all the dimensions associated with an event, as in
Figure 3-11.
Figure 3-11
CUSTOMER
ORDERS
hierarchy chart
Modeling Hierarchy Types
Hierarchy charts
can be annotated to
model ragged,
multi-parent and
variable depth
hierarchies
Ideally, hierarchy charts are used to discover the attribute levels of simple balanced
hierarchies, but they are capable of modeling ragged, multi-parent, and variable
depth hierarchies when necessary. Figure 3-12a shows a hierarchy chart for the
ragged product hierarchy of Figure 3-8. The missing/optional level is enclosed in
brackets. In Figure 3-12b the multi-parent hierarchy (matching Figure 3-9) is
denoted with a double bar between the product child level and its multiple product