Construct the correct physical joins for the virtual table. Notice that CityProductSales2 joins to the Cities and Products tables.

In this example, the two sources comprise the whole domain for soda sales. A domain can have many sources. The sources have to all follow the rule that each level must contain sources that, when combined, comprise the whole domain of values at that level. Setting up the entire domain for each level helps ensure that queries asking for Coke, Pepsi, and 7‐Up don't leave out 7‐Up. It also helps ensure that queries requesting information that has been precomputed and stored in aggregate tables can retrieve that information from the aggregate tables, even if the query requests other information that isn't stored in the aggregate tables.