owlClass

owlClass is a convention used in discussions of the Web Ontology Language (OWL) to denote a class construct. In formal OWL, the official term is owl:Class, and named classes are identified by IRIs. An owlClass represents a set or collection of individuals sharing common characteristics. A class may be primitive or defined by logical conditions; defined classes are specified using class expressions.

The relationships among classes are defined by axioms such as rdfs:subClassOf, owl:equivalentClass, and owl:disjointWith. Complex class expressions combine base classes with restrictions and logical operators, enabling constructs like intersectionOf, unionOf, complementOf, someValuesFrom, allValuesFrom, and cardinality constraints.

Reasoning over an ontology with owlClass allows inferring additional class memberships, detecting inconsistencies, and building class hierarchies. In OWL 2 DL, the language is designed to balance expressivity with decidable reasoning. The open-world assumption and the lack of the closed-world assumption mean that the absence of a statement does not imply its negation.

owlClass is used across tooling and tutorials to illustrate concepts; in actual ontologies, authors declare classes with IRIs and relate them to properties via properties like owl:ObjectProperty and owl:DatatypeProperty. This enables structured categorization of individuals and supports automated reasoning, data integration, and semantic interoperability across systems.