Thursday, June 14, 2012

Creating Oracle BI Presentation Layers from Oracle Cubes

Beginning with Oracle BI, the Oracle BI Administration tool has the ability to import Oracle cubes, dimensions and hierarchies into the Physical layer of the Oracle BI repository.  This provides an alternative to the Oracle BI plug-in for Analytic Workspace Manager.  Each method works somewhat differently and each has certain advantages that might make it the best choice for different situations.

The Oracle BI plug-in for Analytic Workspace Manager pushes metadata into the  Oracle BI repository using UDML code.  The result is a ready to use subject area with the Physical, Business Model and Presentation layers fully built for you.  It creates hierarchies in the Business Model layer, but it does not add hierarchical columns to the Presentation layer.  You can easily add hierarchical columns to the Physical layer by dragging hierarchies from the Business Model layer.

Hierarchical column in the channel dimension.

The Oracle BI plug-in for Analytic Workspace Manager creates a Physical layer that maps to hierarchy and cube views (these views make the dimensions, hierarchies and cubes look like a star schema to SQL).  In the Business Model, it assigns the SUM aggregation operator to measures selected from the cube view.  This approach allows SQL to aggregate data above the cube.  This is useful for queries that first filter and then aggregate and attribute break outs.  For example:

  • Report by Year where Quarter of Year is 3 and 4.  Data at the Year level will be the aggregate of child quarters 3 and 4. 
  • Report by Year, Color and Size where Color and Size are attributes of Item.  Oracle will SELECT year, color, size, SUM(sales) .... GROUP BY year, color, size.

In both cases, Oracle BI will get the highest aggregate level data it can from the cube and do some additional aggregation in SQL.

When cubes are imported using the Oracle BI Administration tool the Physical layer is mapped directly to the cube and dimensions, bypassing the cube and hierarchy views.  The SQL created in this case selects from the OLAP_TABLE table function.  Oracle BI has optimized this SQL to take advantage of some features in OLAP_TABLE, which offers better query performance with hierarchical columns in some situations.

When the cube is imported with the Oracle BI Administration tool, aggregation is set to 'External Aggregation'.  This will disable the ability to create queries that require aggregation above the cube.  This is good in that it prevents users creating queries that might not work as they expect in some cases, but it prevents filter before aggregate and attribute break out queries.

Also, the import method only creates the Physical layer.  It does not create the Business Model and Presentation layers.  You do that by dragging the Physical layer to the Business Model layer and then dragging the Business Model to the Presentation layer.  That's all quick and easy, but there will be some things you will want to update in the Business Model and Presentation layers.  For example, deleting some columns you don't really need and arranging columns in hierarchical order.  I've posted the paper Creating an Oracle BI Presentation Layer from Oracle Cubes on OTN.  This paper will walk you through the process of refining the Business Model and Presentation layers.

My recommendation is to try each method, learn about the strengths of each and choose which is best for any particular application.  Since all the data comes from the same cube, there's nothing wrong with using both methods.

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