An ontology supplies vocabulary and statements about a domain. OWL 2, one ontology language, represents classes, properties, individuals and logical relationships. A knowledge graph can contain particular people, organizations and their connections.
Example: Person and Organization are classes; worksFor relates a person to an organization. A record that Maya works for Acme describes particular individuals. Separately, entity resolution determines whether two records refer to the same person.
An ontology is not automatically a data-validation gate. OWL uses an open-world assumption: an unstated fact may be unknown rather than false. A missing field need not make an ontology inconsistent. Specify separate validation rules for required input fields.
Sources
- W3C: OWL 2 Web Ontology Language Primer, second edition — Explains domain knowledge, classes, properties, individuals and open-world reasoning; checked October 26, 2026.