Assign each class to the vertex, edge or non-graph type sets based on its kind.

def _split_classes_by_kind(self, class_name_to_definition):
        """Assign each class to the vertex, edge or non-graph type sets based on its kind."""
        for class_name in class_name_to_definition:
            inheritance_set = self._inheritance_sets[class_name]

            is_vertex = ORIENTDB_BASE_VERTEX_CLASS_NAME in inheritance_set
            is_edge = ORIENTDB_BASE_EDGE_CLASS_NAME in inheritance_set

            if is_vertex and is_edge:
                raise AssertionError(u'Class {} appears to be both a vertex and an edge class: '
                                     u'{}'.format(class_name, inheritance_set))
            elif is_vertex:
                self._vertex_class_names.add(class_name)
            elif is_edge:
                self._edge_class_names.add(class_name)
            else:
                self._non_graph_class_names.add(class_name)

        # Freeze the classname sets so they cannot be modified again.
        self._vertex_class_names = frozenset(self._vertex_class_names)
        self._edge_class_names = frozenset(self._edge_class_names)
        self._non_graph_class_names = frozenset(self._non_graph_class_names)