Turns out it's easier to reason with binary relationships so if you only use tables with 2 columns it's somewhat easier to infer things from your data. Categor

Turns out it's easier to reason with binary relationships so if you only use tables with 2 columns it's somewhat easier to infer things from your data. Categories of products is a good example as they form a transitive relation, but not necessarily a strict hierarchy (any particular entity might be in multiple distinct categories).