My first Publication Agile-Data-Warehouse-Design-eBook | Page 100

Modeling Business Dimensions
79
type parents. In Figure 3-12c the variable depth of a human resources (HR) hierar-
chy caused by the recursive relationship (see Chapter 6) between managers and
employees is modeled by adding a circular path between the two levels. These
annotations can be combined to model the most complex hierarchies.
Figure 3-12a, b, c
Ragged,
multi-parent and
variable depth
hierarchy charts
Modeling Queries
Event hierarchy charts which combine multiple dimension hierarchy charts for the
same event can be used to model query definitions for report and dashboard
design. One or more queries can be defined on an event hierarchy chart as lines
connecting the referenced levels, as shown in Figure 3-13 where X marks levels that
are used to filter the query (WHERE clause), and O marks those used to aggregate
it (GROUP BY clause). In this way, event hierarchy charts can also be used to
model the dimensionality of OLAP cubes and aggregate fact tables.
Event hierarchy
charts can model
the dimensionality
of queries, OLAP
cubes and
aggregates
Figure 3-13
Query definition
hierarchy chart
Event hierarchy charts can be used while modeling events to help capture their
major dimensional attributes. By drawing a hierarchy chart above an event table
you can record detail about detail (dimensional attributes) in hierarchical order at
the same time that you model event details (dimensions and facts).