Monday May 03, 2010

OWB 11gR2 – Degenerate Dimensions

Ever wondered how to build degenerate dimensions in OWB and get the benefits of slowly changing dimensions and cube loading? Now its possible through some changes in 11gR2 to make the dimension and cube loading much more flexible. This will let you get the benefits of OWB's surrogate key handling and slowly changing dimension reference when loading the fact table and need degenerate dimensions (see Ralph Kimball's degenerate dimensions design tip).

Here we will see how to use the cube operator to load slowly changing, regular and degenerate dimensions. The cube and cube operator can now work with dimensions which have no surrogate key as well as dimensions with surrogates, so you can get the benefit of the cube loading and incorporate the degenerate dimension loading. What you need to do is create a dimension in OWB that is purely used for ETL metadata;

  • the dimension itself is never deployed (its table is, but has not data)
  • it has no surrogate keys
  • has a single level with a business attribute the degenerate dimension data and a dummy attribute, say description just to pass the OWB validation.

When this degenerate dimension is added into a cube, you will need to configure the fact table created and set the 'Deployable' flag to FALSE for the foreign key generated to the degenerate dimension table. The degenerate dimension reference will then be in the cube operator and used when matching.

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