docs: def load_rml(self, rml_name):
          """ loads an rml mapping into memory
  
          args:
              rml_name(str): the name of the rml file
          """
          conn = CFG.rml_tstore
          cache_path = os.path.join(CFG.CACHE_DATA_PATH, 'rml_files', rml_name)
          if not os.path.exists(cache_path):
              results = get_graph(NSM.uri(getattr(NSM.kdr, rml_name), False),
                                  conn)
              with open(cache_path, "w") as file_obj:
                  file_obj.write(json.dumps(results, indent=4))
          else:
              results = json.loads(open(cache_path).read())
          self.rml[rml_name] = RdfDataset(results)
          return self.rml[rml_name]