dimensional fact model problem

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dimensional fact model problem

Post  ben_1990 on Thu Apr 11, 2013 5:16 pm

Hallo!
I am unexperienced in building a DWH and I hope you can help me

At http://i76.servimg.com/u/f76/18/23/84/53/unbena10.png you can see my (simple) ERM.
The tables A and B are my Dimensions. But what should I do with C?
C has a n:m relationship with B and 1:n relationship with A: a A belongs to ONE C, but a C has serveral A's. For a fact, the C joined over A is identical with the C joined over B. In other words, one fact has exactly one C! It does not matter which "way" (A or B) you use. The relationship between A and C as well as B and C are not important for me. I need A, B and C for aggregation&filtering.

Consequently my intention is to handle C as third Dimension -> "unlink" C from A and B. What do you think about it?

Originally I tried to develop the dimensional fact model using the data driven approach described by Golfarelli et. al. but I didn't find a solution for my construct. I run into the problem that it seems C is a hierarchy instead of dimension. But I think it is nonsense to add the same hierarchy to the dimensions A and B. Why does the data driven approach not working for me- what i'am doing wrong?

Do you know any literature which copes with such a construct?

Thank you!

ben_1990

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Re: dimensional fact model problem

Post  JoaoLains on Tue Apr 23, 2013 11:13 am

Hi there,

To handle many to many relationships i recommend a relationship table (Bridge)
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Re: dimensional fact model problem

Post  ngalemmo on Tue Apr 23, 2013 2:18 pm

Relate C to the fact. There is only one C that would satisfy the situation for a particular fact row, correct?

Facts are held in context with its related dimensions, C being one of them. Relationships A has with C and B has with C are immaterial to the fact. If you want to track the states of relationships between A, B, and C, you use another fact (or facts).
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Re: dimensional fact model problem

Post  ben_1990 on Tue Apr 23, 2013 3:16 pm

Thank you!

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Re: dimensional fact model problem

Post  BoxesAndLines on Tue Apr 23, 2013 10:14 pm

If you did care about the relationships between A, B, and C, you could handle via a factless fact table.
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