Relation pm#subdomain__true-subdomain (domain,domain)  in WebKB-2, ">part" is an abbreviation of this relation since it is not  
 a part relation nor a specialization relation but a mix of both; 
 for details, see http://www.webkb.org/kb/it/o_domain/d_field_of_study.html
  supertype:  relation_from_a_domain__thing_in_domain (domain,?)
     supertype:  domain_related_relation__domain-related-thing (?,?)
        supertype:  relation_playing_a_special_role (*)  this type permits to categorize relations according to their roles ; this is a traditional but quite subjective way of categorizing relations
           >part of:  relation__related_thing__relatedthing___related_with  type for any relation (unary, binary, ..., *-ary) and instance of pm#relation_type
  supertype:  relation_to_a_domain__sub-domain_or_object-subdomain (?,domain)
     supertype:  domain_related_relation__domain-related-thing (?,?)