docs: def _derive_namespaces(self):
  
  		'''
  		Small method to loop through three graphs in self.diffs, identify unique namespace URIs.
  		Then, loop through provided dictionary of prefixes and pin one to another.
  
  		Args:
  			None: uses self.prefixes and self.diffs
  
  		Returns:
  			None: sets self.update_namespaces and self.update_prefixes
  		'''
  
  		# iterate through graphs and get unique namespace uris
  		for graph in [self.diffs.overlap, self.diffs.removed, self.diffs.added]:
  			for s,p,o in graph:
  				try:
  					ns_prefix, ns_uri, predicate = graph.compute_qname(p) # predicates
  					self.update_namespaces.add(ns_uri)
  				except:
  					logger.debug('could not parse Object URI: %s' % ns_uri)
  				try:
  					ns_prefix, ns_uri, predicate = graph.compute_qname(o) # objects
  					self.update_namespaces.add(ns_uri)
  				except:
  					logger.debug('could not parse Object URI: %s' % ns_uri)
  		logger.debug(self.update_namespaces)
  
  		# build unique prefixes dictionary
  		# NOTE: can improve by using self.rdf.uris (reverse lookup of self.rdf.prefixes)
  		for ns_uri in self.update_namespaces:
  			for k in self.prefixes.__dict__:
  				if str(ns_uri) == str(self.prefixes.__dict__[k]):
  					logger.debug('adding prefix %s for uri %s to unique_prefixes' % (k,str(ns_uri)))
  					self.update_prefixes[k] = self.prefixes.__dict__[k]