I need to provide some quick definitions, starting with ontology. It is a rich irony that the word “ontology”, which has to do with making clear and explicit statements about entities in a particular domain, has so many conflicting definitions. I’ll offer two general ones.
The main thread of ontology in the philosophical sense is the study of entities and their relations. The question ontology asks is: What kinds of things exist or can exist in the world, and what manner of relations can those things have to each other? Ontology is less concerned with what is than with what is possible.
The knowledge management and AI communities have a related definition — they’ve taken the word “ontology” and applied it more directly to their problem. The sense of ontology there is something like “an explicit specification of a conceptualization.”
The common thread between the two definitions is essence, “Is-ness.” In a particular domain, what kinds of things can we say exist in that domain, and how can we say those things relate to each other?
Clay Shirky: Ontology is Overrated: Categories, Links, and Tags