Relation rdfs#is_defined_by (?,entity)  in WebKB, pm#definition SHOULD BE USED INSTEAD
  supertype:  see_also__seealso
  equal:  is_defined_by
  subtype:  definition (?,description_content/medium/container)  see also #definition
     subtype:  definition (description_content/medium/container,description_content/medium/container)  a logical relation should be used instead of this relation