Ontology: the study of what there is in the world that we should know about.
Epistemology: the study of how we should get to know the things in the world.
These concepts were in existence long before AI.
When it comes to creating AI we should take an epistemological approach: how does the only working truly intelligent system (the human brain) models the world, innately or by learning. This is in contrast with the ontological approach: focusing on organizing what we know in data ontologies and then trying to instill those in computers.
Briefly, an Ontology is a specification of a conceptualization - and Epistemology is the study of knowledge acquisition.
My favourite:
Artificial intelligence is no match for natural stupidity