def rdf_source(self, aformat="turtle"):
		"""
		Serialize graph using the format required
		"""
		if aformat and aformat not in self.SUPPORTED_FORMATS:
			return "Sorry. Allowed formats are %s" % str(self.SUPPORTED_FORMATS)
		if aformat == "dot":
			return self.__serializedDot()
		else:
			# use stardard rdf serializations
			return self.rdflib_graph.serialize(format=aformat)