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May 3, 2008
How many Dimensions should a data warehouse have?
Of course that will depend on the subject and requirements. However I refuse to believe that a business is / can be analyzed by 100 or even 25 dimensions. There are not simply that many dimensions.
Then why do I see models with 150 dimensions (e.g. in a big stock exchange). What is the mistake that the data warehouse architect made?
Analyzing the dimensions I find they are not dimensions and lookups fitted into dimensional model. A lookup is a code that has a description attached to it. Basically the origin is the transactional systems where there is a need to abbreviate and minimize the transaction length. I would prefer to convert them entirely from codes to proper names. The codes and descriptions are not dimensions.
This got the stock exchange model to less than 15 dimensions easily manageable and understandable. However it was too late to make the change 2 years and 10 million into the project.
The minute you hear the number of dimensions to be a large number - question your data warehouse architect and get a second opinion.
Posted by Vijay at May 3, 2008 7:30 PM
