Parent-child relationship I

Attributes can be related to each other (like in the case of city, province, and country) to form relationships between them. Furthermore, the tables holding attribute data can be normalized, as in the DimProduct, DimProductSubcategory, and DimProductCategory or denormalized as in the DimGeography table where we have province and country names repeated in every row. It is important that foreign keys are in place to preserve data integrity and help the RDBMS use the less expensive query path. So, for example, we have in the DimProductSubcategory table a foreign key pointing to the primary key in the DimProductCategory table.

If you look at the content of the DimProduct table, you'll see some records with NULL values in the DimProductSubcategory column; there are no sales transactions for those products, but this is a very common data quality problem. Missing values in foreign keys is something we usually have to deal with. If those products had sales movements...