Adventure Works Explanation
I've been looking at Microsoft's Adventure Works 2012 database. I'd be very interested if there's any information explaining why the tables were created as they are. Some sort of schema overview I guess.
For example:
Why they chose to create a BusinessEntity table as a sort of base class for Person, Employee, etc.
Most of the data is normalized so why they chose to put the CountryRegionCode field into the StateProvince table instead of an ID to a separate table.
Anyway I'm very interested in learning more about the decisions that went into the databases design. Anyone know a resource that goes into this sort of thing?
Answer
I am not aware of any official design documentation for AdventureWorks, but I use to be a trainer and used AdventureWorks databases extensively for demos and labs, so I am pretty familiar with it.
The BusinessEntity table is a classic case of a SuperType/SubType design, which reduces data redundancy, because customers could also become vendors, employees could become customers, and every other combination. Also, it means that you are not storing details related to all entities repeatedly, in separate tables, minimising effort in the event of code changes.
The CountryRegionCode I am not positive about, but I would suspect one of three reasons:
- There are not enough distinct combinations to warrant an additional table at the expense of reporting performance (This could be validated with some simple COUNT(*) GROUP BY statements)
- They wanted it in the same table so that in future they had the flexibility to model a hierarchy structure with hierarchyID (This is the least likeley option)
- It was a normalisation error! (My money is on this option!)