Multiple Bridge tables to a single fact?

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Multiple Bridge tables to a single fact?

Post  Bumblebee on Sun Aug 23, 2015 9:32 pm

Hi
We have had a design option proposed that has a single fact table, which has 2 bridge tables to multivalued dimensions.

Given that a bridge table changes the grain of the fact table to the level of the bridged multivalued dimension, I would not have thought it was possible to then join a second multivalued dimension to the fact using its own bridge table. Thoughts on this please?

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Re: Multiple Bridge tables to a single fact?

Post  ngalemmo on Sun Aug 23, 2015 9:43 pm

Yes, you can combine multiple bridges in a query. However, unrestricted, you create a cartesian product. This may be significant depending on the cardinality of these relationships. You also need to include an allocation factor for each relationship to distribute measures to the new grain. Multiplying cumulative factors (from the multiple bridges, and provided it is stored as a value between 0..1) to properly allocate the cartesian product before summarization.

If you do allocation, be ready to support multiple allocation factors for different purposes. Allocations tend to be a hot topic among different departments.
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