In which normal form is the dimension table and fact table in the schema?

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  • Jan 21st, 2008

Every schema deals with Facts and Dimensions.

Fact will be the central table in the Schema were as Dimensions Table are the surrounded table of Fact.

Dimensions table is one who give the description of Business Transactions and always having Primary Key .

Fact table is one dealing with Measures and having Foriegn Key.

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Unlike OLTP, the goal of dimensional and fact modeling is not to achieve the highest Normal Form but rather to make key performance indicators (often sought after measures) readily accessible to ad-doc query. 

That being said, Dimensions can strive to be in Boyce-Codd 3rd normal form, while fact tables may be in 1st normal form - having only a primary key being unique. 

De-normalized dimensional tables may be in only 1st normal form but have the advantage of low storage space, while de-normalized 1st normal form dimensional table take more space but perform faster.

In my opinion, this kind of interview question has no single correct answer.  It's a question to get the interviewee to demonstrate their knowledge of normalization and dimensional modeling and the pros and cons of normalization and de-normalization with respect to query speed vs. physical storage.

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