OWL DL allows annotations on classes, properties, individuals and ontology headers, but only under the following conditions:

• The sets of object properties, datatype properties, annotation properties and ontology properties must be mutually disjoint. Thus, in OWL DL dc:creator cannot be at the same time a datatype property and an annotation property.

• Annotation properties must have an explicit typing triple of the form: AnnotationPropertyID rdf:type owl:AnnotationProperty .

• Annotation properties must not be used in property axioms. Thus, in OWL DL one cannot define subproperties or domain/range constraints for annotation properties.

• The object of an annotation property must be either a data literal, a URI reference, or an individual.

Five annotation properties are predefined by OWL, namely: owl:versionInfo rdfs:label rdfs:comment rdfs:seeAlso rdfs:isDefinedBy