digraph decoder {
  "app"                 [ shape="box"
                          label="Application"
                          color="blue4" ];
  "psi_dec"             [ shape="box"
                          label="PSI decoder"
                          color="red3" ];
  "specific_dec"        [ shape="box"
                          label="Specific decoder"
                          color="green4" ];

  app -> psi_dec -> specific_dec -> app
}