Number of dimensions in a dimensional model.

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Number of dimensions in a dimensional model.

Post  arfoot653@gmail.com on Thu Feb 23, 2012 12:48 pm

In kimball books, 5-15 is recommended limit for the number of dimensions in a dimensional model to avoid centipede design. Does this number consider role playing dimensions as 1 irrespective of how many roles it plays? For ex. if i have an accumulating snapshot and date has 9 roles, should i consider this as 9 or 1? In my accumulating snapshot after combining dimensions wherever possible i have around 13 unique dimensions without considering various roles. If i include roles, it goes to 30 or so with 9 roles for dates, and a couple of other dimensions being role playing dimensions also. Any comments on this?

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Re: Number of dimensions in a dimensional model.

Post  ngalemmo on Thu Feb 23, 2012 3:15 pm

You would count each role. But also realize the 5-15 suggested range is simply that, a suggestion. It doesn't mean a fact cannot or should not have more than 15 dimensions, but rather is a red flag telling you you need to perform a sanity check. Are these dimensions really necessary or have you over-engineered something?
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Re: Number of dimensions in a dimensional model.

Post  BoxesAndLines on Thu Feb 23, 2012 3:25 pm

I've done more than 30 with success (mostly date dimension FK's).
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