Chapter 21. Factless Facts

This chapter teaches you how to deal with a requirement for a measure that is not available in the source data. For example, the product source data (the product.txt file you used in Chapter 2, “Dimension History” and Chapter 8, “Regular Population”) do not contain product count information. If you need to know the number of products in your system, clearly you cannot simply pull this out of your data warehouse.

The factless fact technique can help. By using this technique, you can count the number of products by keeping track of product launches. You can create a factless fact table that has only surrogate keys from the product (what you count) and the date (when the count occurs) dimensions. We call the table a factless table because the table itself does not have a measure.

This chapter shows you how to apply the factless fact technique in your data warehouse.