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data warehouse - star schema

Posted on 2011-02-21
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Hello

I'm just reading/learning about the data warehouse star schema. Lets take what seems to be the canonical example of a star schema, where you have a sales fact table and product/store/customer etc dimension tables. Here is an example from oracle

http://download.oracle.com/docs/cd/B10501_01/server.920/a96520/schemas.htm#12896

 The sales table would have fields such as quantity_sold and cost and then keys for each dimension

I'm getting a bit confused with the traditional 3NF form of this model where you would have a 1:N relationship between customers and orders and a M:M relationship between orders and products. Here is a picture of what i mean

http://download.oracle.com/docs/cd/B10501_01/server.920/a96520/schemas.htm#14651

Using the star schema, what would happen for a sale that had multiple products? Would there be one row per product sold in the central fact table and this row would 'duplicate' the key information  (i.e. each product in the same sale would have the same key for each dimension such as customer/store/date etc)

thanks
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Question by:andieje
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Using the star schema, what would happen for a sale that had multiple products? Would there be one row per product sold in the central fact table and this row would 'duplicate' the key information  (i.e. each product in the same sale would have the same key for each dimension such as customer/store/date etc)

Yes that is correct.

I tend to use a combination of 3NF and Snowflake... I just find that is most flexible.
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by:andieje
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thanks
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