Dimension vs Dimension Attribute

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Dimension vs Dimension Attribute

Post  angelos_T on Wed Jul 23, 2014 5:32 am

Hi,
Does anyone have any useful tips or guidelines on whether an object should remain an attribute of a dimension vs becoming a dimension in its own capacity.
I have always gone with the amount of attributes linked to an object as a rule of thumb.

For example:
I have a Product dimension with an attribute of Product Supplier.
There are currently no other attributes associated with Product Supplier so I'm debating the need to give Product Supplier it's own dimension.

Any thoughts or recommended reading?

Angelos

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Re: Dimension vs Dimension Attribute

Post  nick_white on Wed Jul 23, 2014 6:02 am

I can think of two areas of consideration (others can probably think of more)...

1. Is there always a 1:1 match between the attributes? In your case can the Product only have one supplier?
2. Will the attributes you are considering splitting out out of the dimension ever be used independently of the parent dimension? In your case would you ever want to link the Supplier to a Fact without also linking the product to the fact?

If there is always a 1:1 match then they are a candidate for being in the same dimension, so it's then a decision for you on how you want to model your data. If there isn't a 1:1 relationship then you can't put them in the same Dim and the decision is made for you.

If you will never use Supplier independently from Product then keep them in the same Dim - if you might use them independently then you can consider splitting them into separate Dims - but again the final choice is yours.

In your particular case, if there are no attributes for the Supplier apart from the name, then even if you logically want to split them into separate Dims you would almost certainly make Supplier a degenrate Dim in your fact table(s) rather than creating a physical Dim table with one attribute

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Re: Dimension vs Dimension Attribute

Post  BoxesAndLines on Wed Jul 23, 2014 8:22 am

angelos_T wrote:
...
There are currently no other attributes associated with Product Supplier so I'm debating the need to give Product Supplier it's own dimension.

Any thoughts or recommended reading?

Angelos

When you do have multiple attributes that are dependent on each other, that would be a good time. I would consider any time you also have multiple facts that want to filter on the subset of attributes. Say you have a small set of attributes that folks like to filter on in various reports. The cardinality of these attributes is much lower that the existing product dimension. In this case, there is a compelling reason to break out the attributes into its own dimension.
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Re: Dimension vs Dimension Attribute

Post  angelos_T on Wed Jul 23, 2014 9:57 am

Thanks for the feedback guys.
These are valid points and in my case it looks like a degenerate dim is the way to go since users will frequently want a product supplier view without ever looking at the products.


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