pm#virtual_class__virtualclas  class that should not be used directly: its subtypes should be used instead
  supertype:  class__clas (sumo)  classes differ from sets in three important respects: 1) classes are not assumed to be extensional, i.e. distinct classes might well have exactly the same instances, 2) classes typically have an associated `condition' that determines the instances of the class, e.g., the condition `human' determines the "class of humans" (note that some classes might satisfy their own condition (e.g., the "class of abstract things" is "abstract") and hence be instances of themselves), 3) the instances of a class may occur only once within the class, i.e. a class cannot contain duplicate instances
  subtype:  virtual_relation_type
     instance:  domain_related_relation__domain-related-thing (?,?)
        subtype:  relation_from_a_domain__thing_in_domain (domain,?)
           subtype:  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
           subtype:  domain_object (domain,?)
              subtype:  core_domain_object__central_object_of_domain (domain,?)
        subtype:  relation_from_a_thing_that_is_not_a_domain__thing_in_domain_of_object (thing_that_is_not_a_domain,?)
           subtype:  object_subdomain__subdomain_of_object (thing_that_is_not_a_domain,domain)
           subtype:  object_in_domain_of_object (thing_that_is_not_a_domain,thing_that_is_not_a_domain)  all relations non exclusive with this one are subtypes of this one; this is stated via:
 pm#relation subtype: {(pm#object_in_domain_of_object  pm#relation_from_a_domain pm#object_subdomain)};
        subtype:  relation_to_a_domain__sub-domain_or_object-subdomain (?,domain)
           subtype:  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
           subtype:  subdomain_of_object (?,domain)
        subtype:  relation_to_a_thing_that_is_not_a_domain__domain-related-object (?,thing_that_is_not_a_domain)
           subtype:  domain_object (domain,?)
           subtype:  object_in_domain (?,thing_that_is_not_a_domain)
     instance:  relation_from_a_domain__thing_in_domain (domain,?)
     instance:  relation_from_a_thing_that_is_not_a_domain__thing_in_domain_of_object (thing_that_is_not_a_domain,?)
     instance:  object_in_domain_of_object
     instance:  relation_to_a_domain__sub-domain_or_object-subdomain (?,domain)
     instance:  relation_to_a_thing_that_is_not_a_domain__domain-related-object (?,thing_that_is_not_a_domain)

No statement uses or specializes virtual_class; click here to add one.