IsClassOf

IsClassOf is a binary predicate used in ontology engineering and knowledge representation to express a hierarchical relation between two classes. In typical usage, IsClassOf(C, D) asserts that C is a subclass or specialization of D, meaning that every instance of C is also an instance of D. The relation is functionally similar to rdfs:subClassOf in RDF and is sometimes implemented as a domain-specific alias or as a subproperty in a given ontology.

Semantics and modeling: When IsClassOf(C, D) holds, one can infer that the extension of C is a subset of the extension of D. Inheritance of properties and constraints associated with D often applies to C as well, subject to other ontology axioms. The exact interpretation can vary by ontology, and some schemas use IsClassOf only for documentation or for lightweight schema checks rather than for full logical reasoning.

Examples: IsClassOf(Dog, Animal) expresses that Dog is a subclass of Animal. IsClassOf(Car, Vehicle) similarly indicates that Car belongs to the class Vehicle.

Relation to other terms: IsClassOf is closely related to subclassOf and can be implemented as an alias or subproperty. In OWL or RDFS, the canonical mechanism for this relationship is rdfs:subClassOf (owl:subClassOf in OWL). Some models distinguish between class-level containment (the class of a thing) and class-level inheritance; IsClassOf is typically used in the former sense if defined narrowly.

See also: rdfs:subClassOf, owl:subClassOf, OWL, RDFS, class, instance, type.

Limitations: The meaning of IsClassOf depends on the ontology. Ambiguities or conflicting axioms can arise when multiple inheritance or disjointness constraints are present.