#!/usr/bin/perl
use Data::Dumper;
use XML::Simple;

use strict;
use warnings;

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

__DATA__
<Parameters>
<ParameterGroup ID="Group1">
<Parameter key="Key1">Some Value</Parameter> 
<Parameter key="Key2">Some Value</Parameter> 
<Parameter key="Key3">Some Value</Parameter> 
</ParameterGroup>
<ParameterGroup ID="Group2">
<Parameter key="Key1">Some Value</Parameter> 
<Parameter key="Key2">Some Value</Parameter> 
<Parameter key="Key3">Some Value</Parameter> 
</ParameterGroup>
</Parameters>

##</code><code>##

#!/usr/bin/perl

use XML::Simple;

use strict;
use warnings;

my $xml = { ParameterGroup => [
	{
		ID => 'Group1',
		Parameter => {
			Key1 => {content => 'Some Value'},
			Key2 => {content => 'Some Value'},
			Key3 => {content => 'Some Value'},
		},
	},
	{
		ID => 'Group1',
		Parameter => {
			Key1 => {content => 'Some Value'},
			Key2 => {content => 'Some Value'},
			Key3 => {content => 'Some Value'},
		},
	},
]};

print XMLout($xml,
	RootName => 'Parameters',
	KeyAttr => 'key',
);

##</code><code>##

<Parameters>
  <ParameterGroup ID="Group1">
    <Parameter key="Key1">Some Value</Parameter>
    <Parameter key="Key2">Some Value</Parameter>
    <Parameter key="Key3">Some Value</Parameter>
  </ParameterGroup>
  <ParameterGroup ID="Group1">
    <Parameter key="Key1">Some Value</Parameter>
    <Parameter key="Key2">Some Value</Parameter>
    <Parameter key="Key3">Some Value</Parameter>
  </ParameterGroup>
</Parameters>