preferred method is to instantiate with repository under 'context',
		but prefixes / namespaces can be added for a Resource instance

		adds to self.rdf.prefixes which will endure through create/update/refresh,
		and get added back to parsed graph namespaces

		Args:
			ns_prefix (str): prefix for namespace, e.g. 'dc', 'foaf'
			ns_uri (str): string of namespace / ontology. e.g. 'http://purl.org/dc/elements/1.1/', 'http://xmlns.com/foaf/0.1/'

		Returns:
			None: binds this new prefix:namespace combination to self.rdf.prefixes for use, and self.rdf.graph for serialization

def add_namespace(self, ns_prefix, ns_uri):

		'''
		preferred method is to instantiate with repository under 'context',
		but prefixes / namespaces can be added for a Resource instance

		adds to self.rdf.prefixes which will endure through create/update/refresh,
		and get added back to parsed graph namespaces

		Args:
			ns_prefix (str): prefix for namespace, e.g. 'dc', 'foaf'
			ns_uri (str): string of namespace / ontology. e.g. 'http://purl.org/dc/elements/1.1/', 'http://xmlns.com/foaf/0.1/'

		Returns:
			None: binds this new prefix:namespace combination to self.rdf.prefixes for use, and self.rdf.graph for serialization
		'''

		# add to prefixes
		setattr(self.rdf.prefixes, ns_prefix, rdflib.Namespace(ns_uri))

		# bind to graph
		self.rdf.namespace_manager.bind(ns_prefix, ns_uri, override=False)