docs: def _read_component_definitions(self, graph):
          """
          Read graph and add component defintions to document
          """
          for e in self._get_elements(graph, SBOL.ComponentDefinition):
              identity = e[0]
              # Store component values in dict
              c = self._get_rdf_identified(graph, identity)
              c['roles'] = self._get_triplet_value_list(graph, identity, SBOL.role)
              c['types'] = self._get_triplet_value_list(graph, identity, SBOL.type)
              obj = ComponentDefinition(**c)
              self._components[identity.toPython()] = obj
              self._collection_store[identity.toPython()] = obj