var req = null;

/**
* Diese Funktion wertet die XML Daten aus, die die Fächer und ihre ID enthalten.
*/
function handleSubjects()
{            
  switch(req.readyState) 
  {
    case 4:
      subsub_field = document.getElementById("subsub");
                            
      xml = req.responseXML;
      
      subsub_field.length = 0;
      for (i=0; i<xml.getElementsByTagName("subject").length; i++) 
      {
        text = xml.getElementsByTagName("subject")[i].getElementsByTagName("name")[0].firstChild.nodeValue;
        value = xml.getElementsByTagName("subject")[i].getElementsByTagName("id")[0].firstChild.nodeValue;
        subsub_field.options[i] = new Option(text, value);
      }
    break;
            
    default:
      return false;
      break;     
  }
}

/**
* Diese Funktion beauftragt die Unterfächer als XML Daten aus der Datenbank zu 
* holen.
*/
function getSubSubjects()
{         
  try
  {
    req = new XMLHttpRequest();
  }
  catch (e)
  {
    try
    {
      req = new ActiveXObject("Msxml2.XMLHTTP");
    } 
    catch (e)
    {
      try
      {
        req = new ActiveXObject("Microsoft.XMLHTTP");
      } 
      catch (failed)
      {
        req = null;
      }
    }  
  }

  var url = 'ajax/subsub.php?id='+document.getElementById('mainsub').value;
  req.open("GET", url, true);

  req.onreadystatechange = handleSubjects;
  req.setRequestHeader("Content-Type", "application/x-www-form-urlencoded");
  req.send(null);
}

/**
* Diese Funktion beauftragt die Unterfächer als XML Daten aus der Datenbank zu 
* holen, die mindestens eine Anzeige beinhalten.
*/
function getFilledSubSubjects()
{         
  try
  {
    req = new XMLHttpRequest();
  }
  catch (e)
  {
    try
    {
      req = new ActiveXObject("Msxml2.XMLHTTP");
    } 
    catch (e)
    {
      try
      {
        req = new ActiveXObject("Microsoft.XMLHTTP");
      } 
      catch (failed)
      {
        req = null;
      }
    }  
  }

  var url = 'ajax/subsub.php?filled=true&id='+document.getElementById('mainsub').value;
  req.open("GET", url, true);

  req.onreadystatechange = handleSubjects;
  req.setRequestHeader("Content-Type", "application/x-www-form-urlencoded");
  req.send(null);
}