owlsubClassOf

owl:subClassOf, written with the IRI http://www.w3.org/2002/07/owl#subClassOf, is an OWL object property used to express a subclass relationship between two class expressions. It asserts that every instance of the subclass is also an instance of the superclass, forming a hierarchical taxonomy within an ontology. The relation can be stated between named classes or more complex class expressions (for example, intersections or unions).

In practice, the axiom C owl:subClassOf D says that C is included in D. If x is an instance of C, reasoners can infer that x is also an instance of D. The property is transitive: if C owl:subClassOf D and D owl:subClassOf E, then C owl:subClassOf E. Every class is considered a subclass of itself by the logical semantics (reflexivity of the subsumption relation). The relation is not symmetric; having C owl:subClassOf D does not imply D owl:subClassOf C.

owl:subClassOf is part of OWL’s richer class-expression framework, alongside constructs like owl:equivalentClass, owl:disjointWith, and various restrictions. It complements the simpler RDFS mechanism rdfs:subClassOf, which serves similar purposes in plain RDF schemas but without the same expressive power.

Examples of usage include declaring that :Dog SubClassOf :Mammal in Manchester or RDF/Turtle syntax as :Dog owl:subClassOf :Mammal. Such axioms enable automated reasoning to classify instances, check ontology consistency, and support querying over inferred class memberships.