@Override
public synchronized String addOntology(OntologyInputSource<?,?> ontologySource) throws UnmodifiableOntologyCollectorException {
long before = System.currentTimeMillis();
if (locked) throw new UnmodifiableOntologyCollectorException(this);
log.debug("Adding ontology {} to space {}", ontologySource != null ? ontologySource : "<NULL>",
getNamespace() + getID());
if (ontologySource == null || !ontologySource.hasRootOntology()) // No ontology to add
throw new IllegalArgumentException(