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Oracle Tips
by Burleson Consulting
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The Data Warehouse Development Life Cycle
Data Aggregation And Drill-Down
One of the most fundamental principles of the multidimensional
database is the idea of aggregation. As we know, managers at
different levels require different levels of summarization to make
intelligent decisions. To allow the manager to choose the level of
aggregation, most warehouse offerings have a "drill-down" feature,
allowing the user to adjust the level of detail, eventually reaching
the original transaction data. For obvious performance reasons, the
aggregations are pre-calculated and loaded into the warehouse during
off-hours. (See Figure 6.2.)
Figure 6.2 Levels of pre-aggregation of summary data.
Of the several types of aggregation, the most common is called a
roll-up aggregation. An example of this type of aggregation would be
taking daily sales totals and rolling them up into a monthly sales
table. These types of summaries are easily computed from the base
data warehouse by using the SQL SUM operator.
The more difficult type is the aggregation of boolean and
comparative operators. For example, assume that a salesperson table
contains a boolean column called turkey. A salesperson is a turkey
if his or her individual sales are below the group average for the
day. A salesperson may be a turkey on 15 percent of the individual
days; however, when the data is rolled up into a monthly summary, a
salesperson may become a turkey even if they only had a few (albeit
very bad) sales days.
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