I have recently got familiar with the concept of “Factless Fact Tables”, and due to the fact that it was very interesting for me, I like to share it with you, if you are not already familiar with it.
The “Factless Fact Table” is a table which is similar to Fact Table except for having any measure; I mean that this table just has the links to the dimensions. But what is the benefit?
These tables enable you to track events; indeed they are for recording events.
Another kind of this Table is known as “Factless Coverage Table” which is very usefull. Imagine that you have a retail stores and each store has its own promotion policy. It would be very complicated if you wanted to answer this sort of question: “Which products were on promotion that didn't sell?”
The best way for covering these kinds of questions is the coverage tables. These tables hold the coverage data for answering these questions.
I also recommend reading “Factless Fact Tables” that was written by Ralph Kimball.