def rdf
      return @rdf unless @rdf.nil?
      uri4rdf = @iri.to_s
      tries = 0
      begin
        tries += 1
        @rdf = RDF::Graph.load(uri4rdf)
      rescue
        sleep 1 * tries
        retry if tries < 3
        binding.pry if @@config.debug
        @@config.logger.error("Failed to retrieve RDF for #{uri4rdf}")
        @rdf = nil
      end
    end
def rdf
      return @rdf unless @rdf.nil?
      uri4rdf = @iri.to_s
      tries = 0
      begin
        tries += 1
        @rdf = RDF::Graph.load(uri4rdf)
      rescue
        sleep 1 * tries
        retry if tries < 3
        binding.pry if @@config.debug
        @@config.logger.error("Failed to retrieve RDF for #{uri4rdf}")
        @rdf = nil
      end
    end
Retrieve RDF graph from iri; the results may be cached when
 the RDF::Graph.load method uses RestClient and it is configured
 to cache results.
 This method is often overloaded in subclasses because
 RDF services use variations in the URL 'extension' patterns.
 @return [RDF::Graph|nil] an RDF graph