#! perl
use strict;
use warnings;
use XML::Simple;

my $xml       = do { local $/; <DATA>; };
my $xml_Event = XMLin($xml);

for (keys %{ $xml_Event->{attribute} })
{
    printf "'%s' is %srequired\n", $_,
           $xml_Event->{attribute}{$_}{required} =~ /true/i ? '' : 'not ';
}

__DATA__

<Event name="Constants" id="0" ui-visible="0" version="0" serviceKey="0" rateTableName="">
    <properties>
        <visible> false </visible>
    </properties>
    <attribute identifier="00">
        <name> session_id </name>
        <type> string </type>
        <required> true </required>
        <ilog>
            <alternate> session id in string format </alternate>
            <visible> false </visible>
        </ilog>
    </attribute>
    <attribute identifier="01">
        <name> volume </name>
        <type> int </type>
        <required> false </required>
        <ilog>
            <alternate> the volume </alternate>
            <visible> false </visible>
        </ilog>
    </attribute>
</Event>

##</code><code>##

 0:40 >perl 1313_SoPW.pl
' volume ' is not required
' session_id ' is required

 0:40 >