Create bi-directional statements for object relationships.

def _triplify_object(self, data, parent):
        """ Create bi-directional statements for object relationships. """
        subject = self.get_subject(data)
        if self.path:
            yield (subject, TYPE_SCHEMA, self.path, TYPE_SCHEMA)

        if parent is not None:
            yield (parent, self.predicate, subject, TYPE_LINK)
            if self.reverse is not None:
                yield (subject, self.reverse, parent, TYPE_LINK)

        for prop in self.properties:
            for res in prop.triplify(data.get(prop.name), subject):
                yield res