def _superclasses_for_subject(self, graph, typeof):
        """helper, returns a list of all superclasses of a given class"""
        # TODO - this might be replacing a fairly simple graph API query where
        # it doesn't need to
        classes = []
        superclass = typeof
        while True:
            found = False
            for p, o in self.schema_def.ontology[superclass]:
                if self.schema_def.lexicon['subclass'] == str(p):
                    found = True
                    classes.append(o)
                    superclass = o
            if not found:
                break
        return classes