def update(self, items):
        """
        Updates the dependencies in the inverse relationship format, i.e. from an iterable or dict that is structured
        as `(item, dependent_items)`. The parent element `item` may occur multiple times.

        :param items: Iterable or dictionary in the format `(item, dependent_items)`.
        :type items: collections.Iterable
        """
        for parent, sub_items in _iterate_dependencies(items):
            for si in sub_items:
                dep = self._deps[si]
                if parent not in dep.parent:
                    dep.parent.append(parent)