title: Is a snowflake schema better than a star schema for data mining?
body: <p>I know the basic difference between a star schema and a snowflake schema-a snowflake schema breaks down dimension tables into multiple tables in order to normalize them, a star schema has only one "level" of dimension tables. But the <a href="http://en.wikipedia.org/wiki/Snowflake_schema" rel="nofollow">Wikipedia article</a> for Snowflake Schema says</p>
  
  <p>"Some users may wish to submit queries to the database which, using conventional multidimensional reporting tools, cannot be expressed within a simple star schema. This is particularly common in data mining of customer databases, where a common requirement is to locate common factors between customers who bought products meeting complex criteria. Some snowflaking would typically be required to permit simple query tools to form such a query, especially if provision for these forms of query weren't anticipated when the data warehouse was first designed."</p>
  
  <p>When would it be impossible to write a query in a star schema that could be written in a snowflake schema for the same underlying data? It seems like a star schema would always allow the same queries.</p>