PHP - Guardar en db informacion proveniente de xml

<?xml version="1.0" encoding="iso-8859-1"?>

<list>

    <course>CURSO DE MATEMATICA</course>

    <student cedula="4535453" name="Juan" lastname="Aedo">

        <note>1</note>

        <note>2</note>

        <note>3</note>

    </student>

    <student cedula="43768989"  name="Lisette" lastname="Acuña">

        <note>4</note>

        <note>5</note>

        <note>6</note>

    </student>

    <student cedula="347676453"  name="Cristian" lastname="Aguilar">

        <note>7</note>

        <note>8</note>

        <note>9</note>

    </student>

    <student cedula="5344535"  name="Emilio" lastname="Alvarez">

        <note>10</note>

        <note>11</note>

        <note>12</note>

    </student>

<list>

<?php

$host="localhost";

$user="root";

$pw="";

$db="dbxml";

$contenidoXML = simplexml_load_file("Calificaciones.xml");

$tabla = $contenidoXML ->course ;

$cnx = mysqli_connect($host,$user,$pw,$db) or die ("PROBLEMAS DE CONEXION");

  foreach ($contenidoXML->student as $estudiantes)

  {

      mysqli_query($cnx,"INSERT INTO matematica(Cedula,Nombre,Apellido)VALUES

     ('".$estudiantes['cedula']."','".$estudiantes['name']."','".$estudiantes['lastname']."')");

  }

 echo "REGISTRO EXITOSO"."<br>";

?>