OWL 2 RL — what the reasoner actually entails

OWL 2 RL is a profile of OWL 2 designed for forward-chaining rule-based reasoners. It's sound, complete for its rule set, and decidable in polynomial time. pgRDF runs it via the reasonable crate.

Rules that materialize in practice

The rules that fire in real ontologies — and the kind of implicit knowledge each makes explicit:

Vocabulary	Effect after materialize
rdfs:subClassOf (with closure)	Every instance of a subclass is asserted as a typed instance of every ancestor class. Transitive across the chain.
rdfs:subPropertyOf (with closure)	Every triple using a sub-property is mirrored using each super-property.
rdfs:domain / rdfs:range	Subjects of a property acquire its domain class; objects acquire its range class.
owl:equivalentClass	Class membership is mirrored both ways.
owl:equivalentProperty	Property assertions are mirrored both ways.
owl:inverseOf	(?a p ?b) materializes (?b p⁻¹ ?a).
owl:TransitiveProperty	(a p b), (b p c) materializes (a p c), transitively.
owl:SymmetricProperty	(a p b) materializes (b p a).
owl:sameAs	Property assertions and class memberships are replicated across the sameAs equivalence class.
owl:FunctionalProperty / owl:InverseFunctionalProperty	Drives sameAs consequences when the data implies it.
Class-construction (owl:intersectionOf, owl:unionOf, owl:hasValue, owl:someValuesFrom, owl:allValuesFrom in OWL 2 RL-permitted shapes)	Class membership is inferred where the construction's conditions hold.

What OWL 2 RL deliberately doesn't support

The full set of restrictions defining OWL 2 RL is in the W3C OWL 2 RL profile spec. The cliff-notes version of what's outside the rule set:

• General owl:complementOf reasoning.
• owl:oneOf over uniqueness implications.
• Full description-logic class equivalence (the OWL DL profile is computationally harder and is intentionally not supported here).

If your ontology uses constructs outside OWL 2 RL, those parts of the model don't drive entailments; the rest of the ontology still materializes as expected.

A worked rule

owl:TransitiveProperty is one of the most useful in practice. Given:

ex:partOf rdf:type owl:TransitiveProperty .
ex:tire   ex:partOf ex:wheel .
ex:wheel  ex:partOf ex:car .

After materialize, the graph also contains:

ex:tire   ex:partOf ex:car .

A SPARQL query asking "what is the tire part of?" then returns both ex:wheel and ex:car without your application implementing the transitive closure itself.

Why a project manager cares

OWL 2 RL is the standard the W3C-aligned ontology community publishes against. Ontologists ship ontologies in OWL 2 RL because the rule set is decidable in polynomial time — and pgRDF runs that exact rule set. Application queries written against the surface shape match implicit knowledge without the application carrying the reasoning burden.

See also

• Mental model.
• Worked example.
• docs/04-inference.md — engineering doc.