The good old IBM Data Modeling Techniques for Data Warehousing
Guideline 1: Each fact should have a real-world business equivalent.
Guideline 2: Focus on determining business-related facts that represent either:
− Business transactions or business events or
− Business objects whose state is of interest for the information analyst or
− Business objects whose state changes are of interest for the information analyst
Guideline 3: Each fact should be uniquely identifiable, merely by the existence of its real-life equivalent.
Guideline 4: The granularity of the base dimensions of each fact should be as fine-grained as possible.