Barring a CPAN module (untested code follows, please tell me if this doesn't work -- it may be missing some whitespace in the substitution, for example):

sub stripPOS {
  my $words = shift;
  # rip out any / plus following characters, up to the 
  # first space
  $words =~ s!/\S*!!g;
  return $words;
}
  $sentence =~
    s! \s \<NP\d*\> (.*?) \</NP\> \s ! stripPOS($1). '/NP' !egx;
[download]

Let's break that out:

• s!

  begins the substitution.

• \s \<NP\d*\> \s

  looks for an <NP#> tag between spaces

• (.*?)

  looks for the shortest possible string until...

• \</NP\> \s

  you can find the closing tag

• ! stripPOS($1) . '/NP' !e

  replace it with the POS-stripped version of the stuff in the middle, followed by an /NP "pseudo-POS"

• gx;

  do it everywhere, and make it easier to read

Hope that helps, -- jkahn

Update (ca. 9p GMT-8): I've just realized that this code won't work if there are nested tags, e.g.:

<NP1> <NP2> The/D best/A one/N </NP>
  of/P <NP2> the/D Perl/N Monks/N </NP> </NP>
[download]

Anonymous Monk, does this happen in your input data? I will look at this and see if I can come up with a good answer if it does, or if I feel like it.....

AM might want to consider extract_tagged() in Text::Balanced if s/he needs to cope with recursive NP tags.

Of course - they could always go the whole hog and write a proper parser with Parse::RecDescent... or wait for perl6 rules to arrive :-)

Hello Monk
It does not happen in my input data. There are not nested tags in my sentences. I already run your code, and it works for some of the examples I tried so far.
Thanks

If you can be sure that it will also be in the  <NPx> .. </NP> format, you can use this pseudo-code:

split the sentence on  <NP\d> and  </NP>; remove tags on the even elements; join the sentence elements again.

@parts = split(/<NP.*?>|<\/NP>/, $sentence);
$even = 0;
for $part (@parts) {
    if ($even) {
        $part =~ s/\/\w\w//g;
        $part .= '/NP';
    }
    $even = ! $even;
}
$result = join('', @parts);
[download]

Untested!

Ok. Just replace this

$part =~ s/\/\w\w//g;

by this

$part =~ s/\/\w{2,3}//g;

jkahn's solution below doesn't have this problem. Using his solution it would be:

$part =~ s!/\S*!!g;

Hi Monk
I tested the code and it works well when the tag has only two characters, but it can also has three character

the following was the output for one sentence:

<S> What/WP was/VBD the monetary value /NP of/IN the NobelP PeaceP PrizeP /NP in/IN 1989 /NP ?/./*end-of-sentence*</S>

The original input was:
<S> What/WP was/VBD <NP5> the/DT monetary/JJ value/NN </NP> of/IN <NP6> the/DT Nobel/NNP Peace/NNP Prize/NNP </NP> in/IN <NP7> 1989/CD </NP> ?/./*end-of-sentence*</S>
I tried to change the code but it did not work for two or three How I evaluate the case for two "OR" three characters
Thanks