public Boolean dropGraph(String graphURI) {
			if(graphURI==null){
				log.warning("to be deleted Graph URI is null");
				return false;
			}
			String query = "DROP SILENT GRAPH <"+graphURI+">";
			if(autoCommit){
				return updateIntern(query, true);
			}
			this.queries += query+="\n";
			return null;
	}