def process_rdfgraph(self, rg, ont=None):
        """
        Transform a skos terminology expressed in an rdf graph into an Ontology object

        Arguments
        ---------
        rg: rdflib.Graph
            graph object

        Returns
        -------
        Ontology
        """
        # TODO: ontology metadata
        if ont is None:
            ont = Ontology()
            subjs = list(rg.subjects(RDF.type, SKOS.ConceptScheme))
            if len(subjs) == 0:
                logging.warning("No ConceptScheme")
            else:
                ont.id = self._uri2id(subjs[0])
            
        subset_map = {}
        for concept in rg.subjects(RDF.type, SKOS.Concept):
            for s in self._get_schemes(rg, concept):
                subset_map[self._uri2id(s)] = s
                
        for concept in sorted(list(rg.subjects(RDF.type, SKOS.Concept))):
            concept_uri = str(concept)
            id=self._uri2id(concept)
            logging.info("ADDING: {}".format(id))
            ont.add_node(id, self._get_label(rg,concept))
                    
            for defn in rg.objects(concept, SKOS.definition):
                if (defn.language == self.lang):
                    td = TextDefinition(id, escape_value(defn.value))
                    ont.add_text_definition(td)
                    
            for s in rg.objects(concept, SKOS.broader):
                ont.add_parent(id, self._uri2id(s))
                
            for s in rg.objects(concept, SKOS.related):
                ont.add_parent(id, self._uri2id(s), self._uri2id(SKOS.related))
                
            for m in rg.objects(concept, SKOS.exactMatch):
                ont.add_xref(id, self._uri2id(m))
                
            for m in rg.objects(concept, SKOS.altLabel):
                syn = Synonym(id, val=self._uri2id(m))
                ont.add_synonym(syn)
                
            for s in self._get_schemes(rg,concept):
                ont.add_to_subset(id, self._uri2id(s))
                
        return ont
Transform a skos terminology expressed in an rdf graph into an Ontology object

        Arguments
        ---------
        rg: rdflib.Graph
            graph object

        Returns
        -------
        Ontology