Question: Is there an easy way for me to explain to an ER modeler why facts are in the center of a star schema and not dimensions? For example, I'm being told, if I have Cust, Contract and a Deal Header (with no facts and 300k rows) and a Deal Fact (900k rows). Why wouldn't I have Deal Header as a FACT and Deal FACT could hang off that for performance?
Chuck Kelley's Answer: This is one of those areas where many folks disagree. I believe that (logically) you need to have a Deal Line Item Dimension since the granularity of the Deal FACT is at a level lower than Deal Header. I also believe that the FACT is the intersection (hence the primary key) of all of the required Dimensions (therefore, you require the Deal Line Item Dimension). Physically, I may wish to do that as a single table having the Deal FACT also contain the Deal Line Item Dimension Data. I do not necessarily see the reason for having two equally large tables - 1 FACT and 1 Dimension - but I could accept both ways.
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