If I wanted to create a modelling element such as a class without instances from an input string I would do something like:
OWLEntity entity = factory.getOWLEntity(EntityType.CLASS, IRI.create(input));
The EntityType.CLASS
could be changed to other elements such as EntityType.ObjectProperty
. This is the way I approach this problem and when I want to add instances I just add a new axiom to the ontology manager.