code: public Resource addReference(Reference reference) {
  		Resource resource = this.rdfWriter.getUri(Vocabulary.getReferenceUri(reference));
  
  		this.referenceQueue.add(reference);
  		this.referenceSubjectQueue.add(resource);
  
  		return resource;
  	}
docs: Adds the given reference to the list of references that should still be
  serialized, and returns the RDF resource that will be used as a subject.
  
  @param reference
  the reference to be serialized
  @return RDF resource that represents this reference