Relation sumo#unique_identifier (string,?)  the string uniquely identifies the 2nd argument
  type:  single_valued_relation_type  when an assignment of values to every argument position except the last one determines at most one assignment for the last argument position; not all single_valued_relations are total_valued_relations
  supertype:  names__name (string,?)  the string names the 2nd argument
     supertype:  relation_from_string (string,*)
        supertype:  relation_from_description_content/medium/container (description_content/medium/container,*)
           supertype:  relation_from/to_thing_of_common_kind (*)  this type permits to categorize relations according to their signatures and hence offers (i) a concise way to set essential exclusion relations, and (ii) a systematic and easy-to-follow categorization
              >part of:  relation__related_thing__relatedthing___related_with  type for any relation (unary, binary, ..., *-ary) and instance of pm#relation_type
     supertype:  refers (?,?)  the 1st argument mentions or includes a reference to the 2nd argument, e.g., an article whose topic is a recent change in the price of oil may refer to many other things, e.g., the general state of the economy, the weather in California, the prospect of global warming, the options for alternative energy sources, the stock prices of various oil companies, etc.
        supertype:  Relation (?,?)  to specify a reference to a related resource; in WebKB, pm#relation or MORE PRECISE RELATION TYPES SHOULD BE USED INSTEAD
           supertype:  binary_relation (?,?)  in WebKB, most relation types are binary and some have a variable number of arguments (as in KIF), hence this type is currently only specialized by types that I do not want to see as direct subtypes of pm#relation
              supertype:  relation_with_particular_property (*)  this rather fuzzy type permits to group categorization schemes less common than those covered by the previous sibling categories
                 >part of:  relation__related_thing__relatedthing___related_with  type for any relation (unary, binary, ..., *-ary) and instance of pm#relation_type