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Fact/Dimension - for DW and also DM?

Posted on 2011-02-17
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is the Fact/Dimension way of building database only for Data warehouse or Data Mart also has the same concept?

thanks
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Question by:anushahanna
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by:MIKE
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No

Fact/Dimensions are more based on the KIMBALL methodology, a Data Mart is more inline with INMON methodology.

Basically KIMBALL believes that it is better to build the DATA WAREHOUSE first based on Business Processes and requirements, INMON believes that the DATA MARTS should be build first based on Business Processes/Requirements, then the DW should be based on these data marts.

KIMBALL METHOD = Fact / Dimensions (star schema)
INMON METHOD = DATA MART based on business units/processes.

In my opinion, KIMBALL approach is the more practical way of building Enterprise DW's.

However, the debate is a never-ending one.....

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by:anushahanna
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>>INMON ......then the DW should be based on these data marts.

what specific methodology?

regardless, in both cases, DW ends up with Facts/Dim?
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dportas earned 425 total points
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CRXIuser2005 seems to have his summary of the Ralph Kimball and Bill Inmon approaches the wrong way round.

Kimball's approach is to create data marts. Kimball's view is that a "data warehouse" is nothing more or less than a collection of marts. Kimball's "dimensional" modelling approach is therefore the one he recommends only for building marts. Marts are what dimensional modelling is typically used for. Inmon's approach is to build a DW first and then use that to populate marts. A DW typically uses a Normal Form rather than dimensional approach.

In general in my experience (and as recommended by Bill Inmon) the most successful way to build a data warehouse is a Normal Form design (I suggest at least Boyce Codd / 5th Normal Form). "Dimensional" modelling approaches can work acceptably for simple models with a few dimensions. You could use a dimensional approach to build a large enterprise warehouse but almost by definition it makes the model and the load process much more complex than they need to be. Large dimensional models are very difficult to maintain and refactor and cause significant problems and costs due to the large amount of redundant data they create.

Whereas dimensional models were popular 10 years ago it's fair to say that they are much less so today because its drawbacks are much more apparent and relevant today than they were in the past. My suggestion would be that you consider a Normal Form approach rather than a dimensional one for your DW.

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by:anushahanna
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thanks dportas

>>I suggest at least Boyce Codd / 5th Normal Form

isn't that the max?

>>My suggestion would be that you consider a Normal Form

so that would be like OLTP method, right?
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by:dportas
dportas earned 425 total points
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>> isn't that the max?
5NF eliminates all join dependencies except those implied by superkeys. 6NF and DKNF are somewhat "stricter" though they are less commonly applied.

>> so that would be like OLTP method, right?
Normal Form is a good guiding principle for any type of database workload, yes.
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by:anushahanna
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Thanks for clarifying that, dportas.

what is a dependable reference you use for Bill Inmon method of normal form design?
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by:dportas
dportas earned 425 total points
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Normal Form wasn't invented by Inmon and isn't really a topic in his books but take a look at:

www.inmoncif.com
www.amazon.com/gp/aw/d/0764599445
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by:anushahanna
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helped - thanks very much!
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