Is Cost a Fact?: Design Challengers debate whether item cost amount should reside in the fact table or a dimension

How does the business use book cost? If business questions only reference Book Cost Amount to help describe the books along with other book information such as title, then Book Cost Amount can remain in the dimension. If, however, Book Cost Amount needs to be viewed at similar levels as that of Sales Amount, moving Book Cost Amount to the fact table can enable the user to answer more questions such as this one posed by data architect David Ness: "What is the total cost of all books sold in the Northwest region in April?" If we expand usage to include profit as well as sales, Jan M. Kamil, enterprise data architect, says that profit calculations that require cost information can obtain that information from the dimension table. Data modeler/data warehouse developer Tom Faulkner suggests also expanding our discussion on usage to include whether book cost needs to be viewed as it changes along with other book data elements: "The cost of a book or any inventory item can change over time, so a slowly changing dimension is a good place to keep the cost of an item to track the history of an item's cost."