determine grain by the physical realities of the data's source

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determine grain by the physical realities of the data's source

Post  fahime on Thu Nov 14, 2013 1:55 am

hello
what does this sentence means in kimball book?
"The grain is determined by the physical realities of the data's source"
but I think grain determine by a business process not the data's source.

how do you think?

fahime

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Re: determine grain by the physical realities of the data's source

Post  BoxesAndLines on Thu Nov 14, 2013 10:42 am

I think you should re-read Kimball's book to understand the grain concept and how to define it. Typically I store the data at the lowest grain regardless of the business process. This allow the most flexibility for reporting.
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Re: determine grain by the physical realities of the data's source

Post  fahime on Thu Nov 14, 2013 10:57 am

OK, thanks
can you explain "The grain is determined by the physical realities of the data's source",
what does it mean?

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Re: determine grain by the physical realities of the data's source

Post  BoxesAndLines on Thu Nov 14, 2013 12:09 pm

Sure, the data defines the grain. There is uniqueness in the data based on the columns. When building fact tables, store the lowest uniqueness since this always leaves the ability to aggregate later. Read the chapter on the grocery store. Data is stored at the product level but the business process may want reporting at the ticket level.
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