Scusami io non sono molto esperto sia per il php che per l'xml.
Io l'xml lo ricavo lanciando questo file php:

Codice PHP:
function xmlentities($text)
  {
    $search = array('&','<','>','"','\'');
    $replace = array('&amp;','&lt;','&gt;','&quot;','&apos;');
    return str_replace($search,$replace,$text);   
  }
  print chr(60)."?xml version='1.0' encoding='ISO-8859-1'?".chr(62);
  print chr(60)."channel".chr(62);
  $sql = "SELECT * FROM adss_adss c left join adss_cities cty on cty.cityid = c.ads_city left join adss_zones czones on czones.zones_id = c.ads_zones left join adss_category ccategory on ccategory.category_id = c.ads_category left join adss_shops cshop on cshop.shopid = c.ads_shop where ads_status='A' and zones_id='5' and ads_enddate > now() ";
  $link = @mysql_connect($databaseServer,$databaseUsername,$databasePassword);
  @mysql_select_db($databaseName,$link);
  $result = mysql_unbuffered_query($sql,$link);
  while($row = mysql_fetch_array($result,MYSQL_ASSOC))

  {
    // create the loc (URL) value based on the $row array, for example:

//discount value
$discount = ($row["ads_realvalue"] * ($row["ads_offer"]/100));
$current_amount = $row["ads_realvalue"] - $discount; //current rate of deal

print chr(60)."item".chr(62);

$titolo ="$titolo";
print "<title>".xmlentities($titolo)."</title>";

$descrizione ="$descrizione";
print "<description>".xmlentities ($descrizione)."</description>";

$ads_image =".$ads_image.";
print "<media-thumbnail url='http://www.miosito.it/".$row['ads_image']."'></media-thumbnail>";

print "<ads>";

$ads_createddate =".$ads_createddate.";
print "<startdate>".$row['ads_createddate']."</startdate>";

$ads_enddate =".$ads_enddate.";
print "<enddate>".$row['ads_enddate']."</enddate>";

$value =".$ads_realvalue.";
print "<price>".$row['ads_realvalue']."</price>";

$discount_percent =".$ads_offer.";
print "<discount>".$row['ads_offer']."</discount>";

$termini ="$termini";
print "<terms>".xmlentities ($termini)."</terms>";

print "<owner>";

print "<name>".$row['shopname']."</name>";

print "<tel>".$row['shop_tel']."</tel>";

print "<email>".$row['shop_email']."</email>";

print "<location>";

print "<area>".$row['zones_name']."</area>";

print "<address>".$row['shop_address']."</address>";

print "<city>".$row['cityname']."</city>";

print "<country>Italia</country>";

print "</location>";

print "</owner>";

print "</ads>";

print "</item>";

}

print "</channel>";
?>