Relation pm#relation_from_situation_to_situation (pm#situation,pm#situation)
  exclusion:  pm#relation_from_situation_to_time  pm#relation_from_time_to_situation  pm#relation_to_time  pm#temporal_relation
  subtype:  pm#later_situation  pm#before_situation
  supertype:  pm#relation_from_situation (pm#situation,*)
     supertype:  pm#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:  pm#relation__related_thing__relatedthing___related_with  type for any relation (unary, binary, ..., *-ary) and instance of pm#relation_type
  supertype:  pm#relation_to_situation (*,pm#situation)  in WebKB, prefer using relations "from" a situation
     supertype:  pm#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
  supertype:  pm#when_relation (?,?)
     supertype:  pm#wh-/how_relation (*)  this type permits to categorize relations according to the usual who/what/why/where/when/how questions ; this is a traditional but very subjective and ineffective way of categorizing relations 
        >part of:  pm#relation__related_thing__relatedthing___related_with  type for any relation (unary, binary, ..., *-ary) and instance of pm#relation_type