Relation pm#creator (entity,entity)
  exclusion:  attributive_relation  purpose  has-author  owned-by  owner  owner_of  leader  seller  customer  generator  spatial_origin  exploits  has_purpose  has_purpose_for_agent  measure  attribute  name  Date  value  rdf_reification_relation  support  example  syntax  has-magnitude
  supertype:  attributive_relation  who_relation
  subtype:  Creator (entity,entity)  to specify an entity primarily responsible for making the content of a resource
     subtype:  author (description,causal_entity)
        subtype:  main_author (description,causal_entity)
        subtype:  co-author (description,causal_entity)