@Override
 public void purge() {
   litCache.clear();
   classesByURI.clear();
   objectPropertiesByURI.clear();
   dataPropertiesByURI.clear();
   datatypesByURI.clear();
   individualsByURI.clear();
   annotationPropertiesByURI.clear();
   intCache.clear();
   doubleCache.clear();
   floatCache.clear();
   stringCache.clear();
 }
 @Override
 public OWLAnnotationProperty getOWLAnnotationProperty(IRI iri) {
   return annotationPropertiesByURI.cache(iri, Buildable.OWLANNOTATIONPROPERTY);
 }
 @Override
 public OWLDatatype getOWLDatatype(IRI iri) {
   return datatypesByURI.cache(iri, Buildable.OWLDATATYPE);
 }
 @Override
 public OWLNamedIndividual getOWLNamedIndividual(IRI iri) {
   return individualsByURI.cache(iri, Buildable.OWLNAMEDINDIVIDUAL);
 }
 @Override
 public OWLDataProperty getOWLDataProperty(IRI iri) {
   return dataPropertiesByURI.cache(iri, Buildable.OWLDATAPROPERTY);
 }
 @Override
 public OWLObjectProperty getOWLObjectProperty(IRI iri) {
   return objectPropertiesByURI.cache(iri, Buildable.OWLOBJECTPROPERTY);
 }
 @Override
 public OWLClass getOWLClass(IRI iri) {
   return classesByURI.cache(iri, Buildable.OWLCLASS);
 }