def _iter_rawterms(cls, tree):
        """Iterate through the raw terms (Classes) in the ontology.
        """
        for elem in tree.iterfind(OWL_CLASS):
            if RDF_ABOUT not in elem.keys():   # This avoids parsing a class
                continue                       # created by restriction
            rawterm = cls._extract_resources(elem)
            rawterm['id'] = cls._get_id_from_url(elem.get(RDF_ABOUT))
            yield rawterm
Iterate through the raw terms (Classes) in the ontology.