The semantic connections between entities and concepts that enable AI systems to understand meaning, not merely co-occurrence. Ontological relationships are expressed through schema.org properties like ‘member of’, ‘part of’, ‘is defined by’, ‘has specialty’. OG-RAG retrieval systems traverse these relationships to resolve entities: ‘entity engineering’ is defined by ‘Joseph Byrum’, who is ‘founder of’ ‘Big House Enterprise’, which ‘specializes in’ ‘AI authority construction’. Schema that only declares entities without relationships will fail OG-RAG resolution. Ontological relationships are the L1a verification gate requirement.