Standard Fedora relations to be included in
        :meth:`index_data` output.  This implementation includes all
        standard relations included in the Fedora relations namespace,
        but should be extended or overridden as appropriate for custom
        :class:`~eulfedora.models.DigitalObject` classes.

def index_data_relations(self):
        '''Standard Fedora relations to be included in
        :meth:`index_data` output.  This implementation includes all
        standard relations included in the Fedora relations namespace,
        but should be extended or overridden as appropriate for custom
        :class:`~eulfedora.models.DigitalObject` classes.'''
        data = {}
        # NOTE: hasModel relation is handled with top-level object properties above
        # currently not indexing other model rels (service bindings)
        for rel in fedora_rels:
            values = []
            for o in self.rels_ext.content.objects(self.uriref, relsextns[rel]):
                values.append(force_text(o))
            if values:
                data[rel] = values
        return data