Conformed Dimensions

[informer30]

Hi All,

I am new to Dimensional modelling and wanted to know in basic terms, what is a conformed dimension?

Many Thanks

 

[r937]

two seconds on google, and here are the first two results --

Dimensions are conformed when they are either exactly the same (including keys) or one is a perfect subset of the other.
--

http://en.wikipedia.org/wiki/Dimension_(data_warehouse)

A conformed dimension is a set of data attributes that have been physically implemented in multiple database tables using the same structure, attributes, domain values, definitions and concepts in each implementation.
--

http://data-warehouses.net/glossary/conformeddimensions.html

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[informer30]

This is the part that confuses me....if one dimension is exactly the same as the other dimension then why have two dimensions the same?

Or am I missing something very obvious here?

Thanks

 

[RiverGuy]

I use the definition found here when referring to a conformed dimension:

A simple answer is that a conformed dimension is a dimension that is shared across fact tables.

http://dylanwan.wordpress.com/2007/01/18/what-is-a-conformed-dimension/

You don't need to have multiple tables, you simply need to have a dimension that works the same way within your data warehouse. So for example, your Location dimension would be designed so that it may support both your Sales data mart as well as your GL data mart. You would need multiple physical dimensions if your data marts were physically separated, or if you have declared a view for a role-playing dimension based off of your core dimension.