docs: def url(self):
          """
          URL of document on ProvStore
  
          :Example:
            >>> stored_document.url
            'https://provenance.ecs.soton.ac.uk/store/documents/148'
          """
          if not self.abstract:
              return "%s/documents/%i" % ("/".join(self._api.base_url.split("/")[:-2]), self.id)