def add_reference(self, subj: Node, val: str) -> None:
        """
        Add a fhir:link and RDF type arc if it can be determined
        :param subj: reference subject
        :param val: reference value
        """
        match = FHIR_RESOURCE_RE.match(val)
        ref_uri_str = res_type = None
        if match:
            ref_uri_str = val if match.group(FHIR_RE_BASE) else (self._base_uri + urllib.parse.quote(val))
            res_type = match.group(FHIR_RE_RESOURCE)
        elif '://' in val:
            ref_uri_str = val
            res_type = "Resource"
        elif self._base_uri and not val.startswith('#') and not val.startswith('/'):
            ref_uri_str = self._base_uri + urllib.parse.quote(val)
            res_type = val.split('/', 1)[0] if '/' in val else "Resource"
        if ref_uri_str:
            ref_uri = URIRef(ref_uri_str)
            self.add(subj, FHIR.link, ref_uri)
            self.add(ref_uri, RDF.type, FHIR[res_type])
Add a fhir:link and RDF type arc if it can be determined
        :param subj: reference subject
        :param val: reference value