my %data_map;
foreach (@data) {
   my ($class, $stamp) = split /\!/, $_;
   $data_map{$class} = $stamp;
}

foreach my $elem (@ref) {
   my ($class, $subcalss, $stamp) = split /:\|/, $elem;
   push @set, "$class:$subclass"
      if $data_map{$class} != $stamp;
}