sauoq is right, P::RD is not needed here, just a pair of regular expressions. Specifically, 
my %data;

while (<DATA>) {
   chomp;

   if (/^JOB ID=(\S+) DESC='(\S+)'/) {
      my $id   = $1;
      my $desc = $2;
      $data{$id} = {
         desc => $desc,
         pred => [],
      };
   } else {
      my ($id, $pred) = (split(/\s+/))[0, 2];
      push(@{$data{$id}{pred}}, $pred);
   }
}

require Data::Dumper;
print(Data::Dumper::Dumper(\%data));

__DATA__
JOB ID=EX1J DESC='JOB1'
JOB ID=EX2J DESC='JOB2'
JOB ID=EX3J DESC='JOB3'
JOB ID=EX4J DESC='JOB3'
EX4J PRED EX2J
EX3J PRED EX1J
EX4J PRED EX1J

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In reply to Re: Best way to sort these strings ? recursive way ? use Parse::RecDescent? by ikegami
in thread Best way to sort these strings ? recursive way ? use Parse::RecDescent? by bertigo

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