Relation pm#relation_from_string (string,*)
  supertype:  relation_from_description_content/medium/container
  subtype:  names__name (string,?)  the string names the 2nd argument
     subtype:  unique_identifier (string,?)  the string uniquely identifies the 2nd argument
  subtype:  related_external_concept (string,?,language)  used to signify a three-place relation between a concept in an external knowledge source, a concept in the SUMO, and the name of the other knowledge source
     subtype:  synonymous_external_concept (string,?,language)  the 2nd argument has the same meaning as the 1st in the language denoted by the 3rd argument
     subtype:  subsumed_external_concept (string,?,language)  the 2nd argument is subsumed by the 1st in the language denoted by the 3rd argument
     subtype:  subsuming_external_concept (string,?,language)  the 2nd argument subsumes the 1st in the language denoted by the 3rd argument