Thanks dasgar for sample input. I have used XML::Twig and xpath expression to do this.

use strict;
use warnings;
use XML::Twig;

my $twiga=XML::Twig->new();    # create the twig for data1
$twiga->parsefile( 'data1.xml'); # build it

my $twigb=XML::Twig->new();    # create the twig for data2
$twigb->parsefile( 'data2.xml'); # build it

foreach my $t ($twiga->get_xpath('//host[@id]')) {
    my $att = $t->{'att'}->{'id'};
    unless ($twigb->get_xpath("//host[\@id='$att']")) {
        print "$att is not found in data2.xml\n";
    }
    foreach my $alias ($t->findnodes("host-alias")) {
        my $web = $alias->text;
        unless ($twigb->get_xpath("//host[\@id='$att']/host-alias[stri
+ng()='$web']")) {
            print "$att with $web is not found in data2.xml\n"
        }
    }
}
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