Knowledgebase
Snowflake schema
Posted by Vladimir Lyutetsky on 20 March 2007 07:04 AM

 

The snowflake schema is a kind of the star schema warehouse model, but a more complex one in comparison to a typical star schema. Graphical representation of the schema resembles a snowflake, hence the name.

Snowflake schemas normalize dimensions to eliminate redundancy. That is, the dimension data are grouped into multiple tables instead of a single large one. For example, a product dimension table in the star schema may only be normalized into a "Product" table, but in the snowflake schema – into a "Product_Category" and a "Product_Manufacturer" tables. While this saves space, it increases the number of dimension tables and requires more foreign key joins. The result is more complex queries and reduced query performance.

The figure below is a graphical representation of a snowflake schema.

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