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}