> The two halves of a [[Description Logic|description logic]] knowledge base: the **TBox** (terminological) holds the schema - concepts and the axioms relating them - and the **ABox** (assertional) holds facts about named individuals. The [[Ontology|ontology]] / [[Intention|intensional]] layer paired with the instance / [[Extension|extensional]] layer a [[Knowledge graph|knowledge graph]] populates. ^definition The TBox states what *can* be true - "a `Manager` is an `Employee`", "every `Parent` has at least one `Child`" - without asserting any individual exists. The ABox states what *is* true of specific things - "`Rex` is a `Dog`", "`Alice` manages `Bob`". The split is what makes reasoning possible: a reasoner reads the ABox against the TBox to check the facts for consistency and to infer what they entail but never state outright. The arrow runs one way - the ABox is typed by the TBox, never the reverse.