#!/usr/bin/perl

use strict;
use warnings;

# use module
use XML::Simple;
use Data::Dumper;

our %pubmed_data;

my $xml = new XML::Simple (KeyAttr=>[]);

my $data = $xml->XMLin("data1.txt");

traverse( $data );

sub traverse {
    our %pubmed_data;
    my ($element) = @_;
    if( ref( $element ) =~ /HASH/ ) {
        foreach my $key (keys %$element) {
            traverse( $$element{$key} );
            }
    } 
    elsif( ref( $element)  =~ /ARRAY/ )  {
        traverse( $_ ) foreach @$element;
    } 
    else {
        if (exists $pubmed_data{$element} ) {
            $pubmed_data{$element}++;
            
            }
        else {
            $pubmed_data{$element} = 1;
            }
    }
}

##</code><code>##

<AuthorList CompleteYN="Y">
                <Author ValidYN="Y">
                    <LastName>Miller</LastName>
                    <ForeName>S I</ForeName>
                    <Initials>SI</Initials>
                </Author>
</AuthorList>