Relation dc#Creator (pm#entity,pm#entity)  to specify an entity primarily responsible for making the content of a resource
  supertype:  pm#creator (pm)
  subtype:  pm#author (pm#description,pm#causal_entity)
     subtype:  pm#main_author (pm#description,pm#causal_entity)
     subtype:  pm#co-author (pm#description,pm#causal_entity)