implementing junk dimension

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implementing junk dimension

Post  VJ09 on Sun Jul 29, 2012 6:54 pm

Hi everyone, I am new to DW and have an implementation question regarding a junk dimension.

I have a junk dimension with a 15 Y/N flags. Total number of rows for all possible combinations of these flags is around 32,000. Of those only 57 combinations are being used by the facts. So I want to just load these 57 rows in the junk dimension and use those foriegn keys for loading the fact table.

The question is when a new fact arrives with a new combination of these flags, how to create a new row in the dimension and get the key populated into the fact table for that fact using SSIS or SQL. I mean I want to generate the dimension rows as and when they are needed as opposed to having them all created ahead of time. I dont know if thats OK

Hope someone can help me with this

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Re: implementing junk dimension

Post  BoxesAndLines on Mon Jul 30, 2012 9:12 am

You load dimensions before you load fact tables. When the new dimension row comes in, insert it. When you load your fact table, the dimension row will be there.
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Re: implementing junk dimension

Post  warrent on Tue Aug 14, 2012 2:25 pm

The problem is you might not know about new combinations for the junk dimension until you start loading the fact table. One approach is to pre-scan the incremental fact rows to find new combinations and add them to the junk dimension. See Design Tip #113 for more specifics:
http://www.kimballgroup.com/html/09dt/DT113CreatingUsingMaintainingJunkDimensions.pdf
--Warren
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Re: implementing junk dimension

Post  Steveo250k on Tue Dec 18, 2012 11:05 am

Where is this file: DT113CreatingUsingMaintainingJunkDimensions.pdf? The link http://www.kimballgroup.com/html/09dt/DT113CreatingUsingMaintainingJunkDimensions.pdf is broken.

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Re: implementing junk dimension

Post  hang on Tue Dec 18, 2012 5:13 pm

It's here: http://www.kimballgroup.com/2009/06/03/design-tip-113-creating-using-and-maintaining-junk-dimensions/

Tell you what, if it's only 32,000 with Y and N, I would not bother to maintain the junk dimension as it's a very small dimension for a lot of attributes. I would just prebuild by cross joining Y and N sets.

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