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AdventureWorksDW2008 - dimension table references other dimension table

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Post  JimmyRichards Sat Mar 24, 2012 1:31 pm

In AdventureWorksDW2008, one of the dimension tables, DimCustomer references DimGeography via the column GeographyKey. Does this break the Kimball and star schema rules for data warehouse design? If it was designed according to Kimballís rules, wouldnít the DimGeography details be listed in DimCustomer in a denormalized structure, so you wouldnít have to join with DimGeography at all? Am I right about this or am I missing something? If I am correct about this, does this make it bad design or just an alternative design?

Thank you!!

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Post  ngalemmo Sat Mar 24, 2012 10:14 pm

Yes, its a snowflake. Its not ideal. If you want to avoid a snowflake you would put the geography attributes in the customer dimension.
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Post  John Simon Sun Mar 25, 2012 9:59 pm

It's actually an Outrigger. The SalesTerritory dimension also has a GeographyKey.

So it's actually in accord with the Kimball approach.

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Post  ngalemmo Mon Mar 26, 2012 12:54 am

Outrigger, snowflake, it's still a dimension with a FK to another dimension. Also, Kimball isn't against it (I don't think he is 'against' anything), it's just that it should be used if appropriate for the situation. In fact, he has published situations where snowflaking is recommended.
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Post  Vishy Mon Mar 26, 2012 2:08 am

If you have aggregate totals on territory then go by this design and have territory independant dim having S.key in the fact.

If you have very big customer dim then again you should go by this design as it won't bloat the customer dim.

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