how many dimensions is too many

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how many dimensions is too many

Post  lconsalvo on Fri Aug 06, 2010 4:56 pm

If I have a fact table with too many dimensions --- over 30, does that mean I've created dimensions when they could have been attributes to another dimension table or possibly that I am trying to capture too many business processes within one fact table.

the problem I am having is at this point i havent been given anything but a list of column names that will be provided from an external vendor (this is our source) and I am trying to do a first pass by mapping the column names to a dimension and a fact. My one fact is a detail/transactional fact table for an origination loan. I am thinking about breaking the detail table into various tables (loan detail, loan foreclosure, Equity Loan). I am also thinking about removing some dimensions that I have identified for code attributes and make them part of the loan dimension. Some of the code dimensions i have design actually hold 1 or 2 values. My thought process was that if they wanted to ever use them in a drop down it would be better to have them as their own dimension rather an attribute to the loan dimension.

Any thoughts?

thanks.

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Re: how many dimensions is too many

Post  ngalemmo on Fri Aug 06, 2010 5:08 pm

If you have separate dimensions for various code/value pairs that make more sense to be on another dimension then, yes, you have far too many dimensions.

Don't make these dimensions simply because you want to provide drop down lists. If you need little tables to provide efficient drop-down list, have a bunch of little tables to do that, but don't make them part of the star schema the end user queries. Put the same code value pairs in the appropriate dimension where they belong.
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Re: how many dimensions is too many

Post  BoxesAndLines on Mon Aug 09, 2010 6:16 pm

Avoid building a loan dimension if at all possible. The dimension will be 1-1 with your fact table. I'm confused on what you are trying to build. If you are building a loan origination data mart, what would you populate with loan foreclosure and equity loan?
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