@sun @lnxw37j1 owl defines itself as inheriting from (subclassOf) rdfs stuff, so you can use just owl if you want (with rdfs things sprinkled in like label/comment/domain/range/subClassOf/subPropertyOf), but some more limited ("owl lite" and "owl dl") inferencers will not be able to pick up on equivalences in certain cases. so it matters to them that you need to subclass from owl:Class, because rdfs:Class is not enough

"owl full" doesn't have this issue iirc