A snowflake dimension is a dimension that is created using a set of dimension tables. A snowflake dimension normally suggests that the tables in the data source have been normalized. Normalization is the process by which tables of a relational database are designed to remove redundancy and are optimized for frequent updates. Most database design books, including The Data Warehouse Toolkit by Ralph Kimball (Wiley, 1996) and An Introduction to Database Systems by C. J. Date (Addison Wesley, 2003), talk about the normalization process in detail.
The columns from different tables of a snowflake dimension often result in levels of a hierarchy in the dimension. The best way to understand a snowflake dimension is to create one yourself. To create one you're going to need two additional tables added to your DSV. Here is how to add the two tables:
Open the AdventureWorksDW DSV and click the Add/Remove Tables button (top-left button in the DSV).
Click DimProductCategory, then Control-Click DimProductSubcategory, then click the right arrow > to move the two tables from the source to the DSV and click OK.
The DSV Designer identifies the relationships defined in the relational backend and shows the relationships between the DimProduct, DimProductSubCategory, and DimProductCategory tables within the DSV Designer graphical design pane. Now that you have the necessary tables in the DSV and the relationships and logical primary keys defined, you can create a ...