Ontologies And Knowledge Bases: Towards A Terminological Clarification / quote 3 of 5
Ontological theory
An ontological theory contains formulas which are considered to be always true (and therefore sharable among multiple agents), independently of particular states of affairs. Formally, we can say that such formulas must be true in every possible world. [...] an ontological theory differs from an arbitrary logical theory (or knowledge base) by its semantics, since all its axioms must be true in every possible world of the underlying conceptualization. This means that while an arbitrary logical theory (containing for instance a statement like apple(a)_pear(a), expressing uncertainty about the object a) may represent a particular epistemic state, an ontological theory can be only used to represent common knowledge independent from single epistemic states.