private function check_presence($uri, $item_id = NULL)
{
$uri = Alias::sanitize($uri);
$item_cond = $item_id !== NULL ? 'AND item_id != ' . (int) $item_id : '';
$sql = 'SELECT DISTINCT alias_id FROM ' . ALIASES_TABLE . ' WHERE uri = "' . $uri . '" ' . $item_cond;
$result = db_query($sql);
return (bool) db_num_rows($result['resource']);
}