docs: def ToURN(self):
      """Converts a reference into an URN."""
  
      if self.path_type in [PathInfo.PathType.OS, PathInfo.PathType.TSK]:
        return rdfvalue.RDFURN(self.client_id).Add("fs").Add(
            self.path_type.name.lower()).Add("/".join(self.path_components))
      elif self.path_type == PathInfo.PathType.REGISTRY:
        return rdfvalue.RDFURN(self.client_id).Add("registry").Add("/".join(
            self.path_components))
      elif self.path_type == PathInfo.PathType.TEMP:
        return rdfvalue.RDFURN(self.client_id).Add("temp").Add("/".join(
            self.path_components))
  
      raise ValueError("Unsupported path type: %s" % self.path_type)