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One or two fact tables?


One or two fact tables?

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kl25
kl25
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Koen Verbeeck (8/8/2013)
OK, now that I see the data, I think you should have 2 fact tables, because indeed they are at two different grains.


Interesting topic. I've been struggling with a similar, two grains but related dimensions situation. Was coming to the conclusion that two fact tables were needed. Any suggested references for reading more about the use of two fact tables? My attempts to search for/find references were not fruitful.
Koen Verbeeck
Koen Verbeeck
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aaa121 (8/8/2013)
Thanks for your time on this. The conclusion I kept coming to was two fact tables as well.

What did you think about the mini dimension solution for those more frequently changing attributes?


If the risk and premium class have fixed number of combinations, the mini-dimension is probably a good idea.
I do think you'd drop the policy risk dimension though, and add a surrogate key into the fact table(s), so that your policy dimension stays small. This way, the risk/premium class is directly tied to the facts.


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Koen Verbeeck
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kl25 (8/8/2013)
Koen Verbeeck (8/8/2013)
OK, now that I see the data, I think you should have 2 fact tables, because indeed they are at two different grains.


Interesting topic. I've been struggling with a similar, two grains but related dimensions situation. Was coming to the conclusion that two fact tables were needed. Any suggested references for reading more about the use of two fact tables? My attempts to search for/find references were not fruitful.


The Data Warehouse Toolkit by Ralph Kimball would be a good start.
Also check out his regular design tips. For example:

http://www.kimballgroup.com/2013/08/05/design-tip-158-making-sense-of-the-semantic-layer/


How to post forum questions.
Need an answer? No, you need a question.
What’s the deal with Excel & SSIS?
My blog at SQLKover.

MCSE Business Intelligence - Microsoft Data Platform MVP
kl25
kl25
Say Hey Kid
Say Hey Kid (684 reputation)Say Hey Kid (684 reputation)Say Hey Kid (684 reputation)Say Hey Kid (684 reputation)Say Hey Kid (684 reputation)Say Hey Kid (684 reputation)Say Hey Kid (684 reputation)Say Hey Kid (684 reputation)

Group: General Forum Members
Points: 684 Visits: 1875
Koen Verbeeck (8/9/2013)
kl25 (8/8/2013)
Koen Verbeeck (8/8/2013)
OK, now that I see the data, I think you should have 2 fact tables, because indeed they are at two different grains.


Interesting topic. I've been struggling with a similar, two grains but related dimensions situation. Was coming to the conclusion that two fact tables were needed. Any suggested references for reading more about the use of two fact tables? My attempts to search for/find references were not fruitful.


The Data Warehouse Toolkit by Ralph Kimball would be a good start.
Also check out his regular design tips. For example:

http://www.kimballgroup.com/2013/08/05/design-tip-158-making-sense-of-the-semantic-layer/


Been doing a lot of reading in the Toolkit. Clearly haven't gotten to the right section yet. :-D

Have only run into the design tips a few times based on general searches. Looks like I need to do a more thorough look at that section of the kimballgroup site. Thanks so much for both suggestions!
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