Default Levels of Aggregation for Measure Columns

You need to specify aggregation rules for mapped logical columns that are measures. Aggregation should only be performed on measure columns, with the possible exception of the aggregation COUNT and Count Distinct. Measure columns should exist only in logical fact tables.

NOTE:  For multidimensional logical columns, you can set the default aggregation rule to Aggr_External.

You can specify an override aggregation expression for specific logical table sources. This helps the Oracle BI Server take advantage of aggregate tables when the default aggregation rule is Count Distinct. If you do not specify any override, then the default rule prevails.

By default, data is considered sparse. However, on rare occasions you might have logical table source with dense data. A logical table source is considered to have dense data if it has row for every combination of its associated dimension levels. When setting up a aggregate rules for a measure column, you can specify that data is dense only if all the logical table sources to which it is mapped are dense.

CAUTION:  Specifying data is dense when any table source that is used by this column does not contain dense data will return incorrect results.

To specify a default aggregation rule for a measure column

1. In the Business Model and Mapping layer, double-click a logical column.
2. In the Logical Column dialog box, click the Aggregation tab.
3. In the Aggregation tab, complete the following fields.
   • If the aggregation rule will be based on a time dimension, select the Based on dimensions check box.
     The Data is dense check box appears.
   • If all the logical table sources to which this column is mapped are dense, you should select the Data is dense check box.
     CAUTION:  Selecting this check box indicates that all sources to which this column is mapped have a row for every combination of dimension levels that they represent. Checking this box when any table source that is used by this column does not contain dense data will return incorrect results.
   • Select one of the aggregate functions from the Default Aggregation Rule drop-down list.
     The function you select is always applied when an end user or an application requests the column in a query.
4. Click OK.