Crear categorias en un XML

Buenas familia

He creado un carrito de compra, donde todo los productos estan en un XML

Código

<?xml version="1.0" encoding="utf-8"?>
		<listings>
<listing>
<title>Art. 1.1 - Uso excesivo del claxon</title>
<description>Utilizar de forma repetida el claxon</description>
<price>250</price>
<carcel>2</carcel>
<images/>
<url>0</url>
</listing>
<listing>
<title>Art. 1.2 - Giro indebido</title>
<description>Hacer un cambio de sentido pisando la linea continua o en zonas no habilitadas</description>
<price>250</price>
<carcel>2</carcel>
<images/>
<url>1</url>
</listing>
<listing>
<title>Art 1.3 - Circular en sentido contrario</title>
<description>Conductor que cons u vehiculo circula o invade el sentido contrario</description>
<price>500</price>
<carcel>2</carcel>
<images/>
<url>2</url>
</listing>
<listing>
<title>Art 1.4 - Estacionar en zonas no habilitadas y obstruir la cinculacion</title>
<description>Abandonar el vehiculo en medio de la calzada o en zonas en la cueles no proceda</description>
<price>250</price>
<carcel>2</carcel>
<images/>
<url>3</url>
</listing>
<listing>
<title>Art 1.5 - Ignorar las señales de transito</title>
<description>Hcaer caso omiso de las señales verticales</description>
<price>250</price>
<carcel>2</carcel>
<images/>
<url>4</url>
</listing>
<listing>
<title>Art 1.6 - Saltarse un semaforo</title>
<description>Saltarse o no realizar los 3 segundos de parada en un semaforo</description>
<price>400</price>
<carcel>2</carcel>
<images/>
<url>5</url>
</listing>
		</listings>

Para ver los productos en el index he creado un PHP que visualice el xml

Código

<?php
if(!defined('IN_SCRIPT')) die("");
?>
<br/>
<br/>
<div id="resultswrapper">
	<h2 class="pull-left no-margin">
	<?php
	if(isset($_REQUEST["keyword_search"]))
	{
		echo $this->texts["search_results"];
	}
	else
	{
		echo $this->texts["our_ads"];
	}
	?>
</h2>
 
<div class="clearfix"></div>		
 
 
<hr class="no-margin"/>
<br/>
<script src="js/results.js"></script>
 
	<div class="clearfix"></div>
	<div class="results-container">		
 
	<?php	
	$PageSize = intval($this->settings["website"]["results_per_page"]);
 
	if(!isset($_REQUEST["num"]))
	{
		$num=1;
	}
	else
	{
		$num=$_REQUEST["num"];
		$this->ms_i($num);
	}
 
 
	$listing_counter = -1;
 
	$listings = simplexml_load_file($this->data_file);
 
	$price_from = 0;
	$price_to = 0;
	$min_price = 0;
	$max_price = 0;
	$iTotResults = 0;
 
 
	if(isset($_REQUEST["amount"])&&trim($_REQUEST["amount"])!="")
	{
		$_REQUEST["amount"]=preg_replace("/[^\-0-9]/","",$_REQUEST["amount"]);
 
 
		$amount_items=explode("-",$_REQUEST["amount"]);
 
		if(sizeof($amount_items)==2)
		{
			$price_from=$amount_items[0];
			$price_to=$amount_items[1];
		}
 
	}
 
	$script_products="";
	$script_products_carcel="";
	$script_product_prices="";
 
	foreach ($listings->listing as $listing)
	{
		$listing_counter++;
 
		$script_products.="products[".$listing_counter."]=\"".trim($listing->title)."\";\n";
		$script_products_carcel.="carcel[".$listing_counter."]=\"".trim($listing->carcel)."\";\n";
		$script_product_prices.="product_prices[".$listing_counter."]=\"".trim($listing->price)."\";\n";
 
 
 
 
		$current_price = floatval($listing->price);
 
 
		//refine search
		if(isset($_REQUEST["only_picture"])&&$_REQUEST["only_picture"]==1)
		{
			if(trim($listing->images)=="") continue;
		}	
 
		if(isset($_REQUEST["keyword_search"])&&trim($_REQUEST["keyword_search"])!="")
		{
			if
			(
				stripos($listing->title, $_REQUEST["keyword_search"])===false
				&&
				stripos($listing->description, $_REQUEST["keyword_search"])===false
			)
			{
				continue;
			}
		}
 
		if($price_from!=0&&$price_to!=0)
		{
			if($current_price<$price_from) continue;
			if($current_price>$price_to) continue;
		}
		//end refine search
 
 
 
 
 
		if($current_price>$max_price) $max_price=$current_price;
 
		if($min_price==0)
		{
			$min_price=$current_price;
		}
		else
		if($min_price>$current_price)
		{
			$min_price=$current_price;
		}
 
 
		if($iTotResults>=($num-1)*$PageSize&&$iTotResults<$num*$PageSize)
		{
 
			$images=explode(",",$listing->images);
 
			if($this->settings["website"]["seo_urls"]==1)
			{
				$strLink = "product-".$this->format_str(strip_tags(stripslashes($listing->title)))."-".$listing_counter.".html";
			}
			else
			{
				$strLink = "index.php?page=details&id=".$listing_counter;
			}
			?>
 
		<div class="panel panel-default search-result">
				<div class="panel-heading">
					<h3 class="panel-title">
 
						<a href="<?php echo $strLink;?>" class="search-result-title"><?php echo $listing->title;?></a>
 
					</h3>
				</div>
				<div class="panel-body">
					<div class="row">
						<div class="col-sm-8 col-xs-12">
							<div class="details">
 
								<p class="description">
									<?php echo $this->text_words(strip_tags($listing->description),80);?>
								</p>
 
								<?php
								if(trim($listing->price)!="")
								{
								?>
 
									<span class="listing-price"><?php echo $this->texts["price"];?>: <strong><?php echo $this->settings["website"]["currency"].number_format(floatval($listing->price), 0);?></strong></span>
 
								<?php
								}
								?>
									<?php
								if(trim($listing->carcel)!="")
								{
								?>
 
									<span class="listing-price"><?php echo $this->texts["carcel"];?>: <strong><?php echo $this->settings[""]["currency"].number_format(floatval($listing->carcel), 0);?> meses</strong></span>
 
								<?php
								}
								?>
 
								<span class="is_r_featured"></span>
							</div>
						</div>
					</div>
					<div class="row">
						<div class="col-xs-6">
 
						</div>
						<div class="col-xs-6">
							<div class="text-right">
								<a class="btn btn-md btn-info" href="javascript:AddToCart(<?php echo $listing_counter;?>)"><?php echo $this->texts["add_to_cart"];?></a>
							</div>
						</div>
					</div>
				</div>
			</div>
			<?php
 
 
		}
 
		$iTotResults++;
	}
	?>
	</div>
	<div class="clearfix"></div>	
</div>	
 
<script>
var currency_symbol="<?php echo $this->settings["website"]["currency"];?>";
var currency_code="<?php echo $this->settings["website"]["currency_code"];?>";
var pp_address="<?php echo $this->SimpleEncrypt("123", $this->settings["website"]["admin_email"]);?>";
var products=Array();
<?php echo $script_products;?>
var product_prices=Array();
<?php echo $script_product_prices;?>
</script>
 
<script>
var min_price=<?php echo $min_price;?>;
var max_price=<?php echo $max_price;?>;
</script>
 
<?php
$this->Title($this->texts["our_ads"]);
$this->MetaDescription("");
?>
 
 
 
<div id="loadmoreajaxloader" style="display:none;"><center><img src="images/loading.gif" /></center></div>
 
 
<script type="text/javascript">
var page_num=2;
$(window).scroll(function()
{
    if($(window).scrollTop() == $(document).height() - $(window).height())
    {
        $('div#loadmoreajaxloader').show();
        $.ajax({
        url: "load_products.php?num="+page_num+"&view="+current_view,
        success: function(html)
        {
            if(html)
            {
                $("#resultswrapper").append(html);
                $('div#loadmoreajaxloader').hide();
				page_num++;
            }else
            {
                $('div#loadmoreajaxloader').html('');
            }
        }
        });
    }
});
 
$(document).ready(function()
{
	InitCart();
});
</script>

No se mucho de PHP, mi preguntas es, se puede agregar algo en el XML como <categoria>1</categoria>
<categoria>2</categoria>
y que en el PHP poner que si la categoria es 1 que muestre ese producto y si es 2 que muestre solo los producto 2?