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A definition for "Dimension" in Analysis Services / OLAP

Posted on 2009-02-24
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Hello:

In the Glosary of the BOLs of the SQL Server 2005 you can find the following definition for "Dimension" in Analysis Services:

"A structural attribute of a cube, which is an organized hierarchy of categories (levels) that describe data in the fact table. These categories typically describe a similar set of members upon which the user wants to base an analysis. For example, a geography dimension might include levels for Country, Region, State or Province, and City."

I have a doubt with regard of this: What is really a Dimension?

If you take the first words ("A structural attribute of a cube") a dimension seems to be just an attribute, in concrete the key attribute, it is, the attribute related to the PK in the dimesion table.

But if you think about the following words ("which is an organized hierarchy of categories (levels)..."), it seems that a dimension comprises the whole set of attributes derived from the dimension table.

I think that clear defiitions are very important for any discipline, and that there are not good unified ones for OLAP. What do you think?

Juarrero
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Question by:juarrero
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by:RWrigley
ID: 23724749
I think you need to read a good book on data warehousing concepts, with emphasis on books written by Ralph Kimball (the father of OLAP) or Bill Inmon (the father of data warehousing).  This will make it easier to understand how and why specific vendors have designed their products.  
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TommyTupa earned 375 total points
ID: 23809474
I don't find that the statement conflict with one another, a cube needs a dimension to be called a cube, hence a dimension is a structural attribute of the cube.  A dimension is composed of related attributes.  Each dimension can be part of a hierarchy.  

I believe that you're on to something in that terminology is often confusing for no good reason and mis-leading and if you're not within the field you'll go bonkers trying to understand what people are saying.   The author (kimball) mentioned above has a set of rules and methods and examples which standardize things.

As for the definition of dimension, its simply a lookup table.    
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Author Closing Comment

by:juarrero
ID: 31572179
I think this is the more complete answer.

I would have liked to split the points, but I do not know how to do it.

Thanks everyone..

Juarrero
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