var req;

function Init ()
{
  var select = document.getElementById ("DateSelecter");
  select.onchange = UpdatePresentation;
}

function UpdatePresentation ()
{
  var select = document.getElementById ("DateSelecter");
  if (select.value != "")
    loadXMLDoc ("Presentations.php?Date=" + select.value);
}

function processReqChange ()
{
  if (req.readyState == 4) {
    if (req.status == 200) {
      // add the data to the interface
      ReplacePresentation (req.responseXML);
    } else {
      alert ("there was a problem retrieving XML: " + req.statusText);
    }
  }
}

function ReplacePresentation (xml)
{
  var div = document.getElementById ("PresentationDiv");
  var Titles = xml.getElementsByTagName ("Title");
  var Speakers = xml.getElementsByTagName ("Speaker");

  div.innerHTML = Speakers[0].firstChild.nodeValue 
                + " is speaking on " 
                + Titles[0].firstChild.nodeValue;
}

// Apple XMLHttpRequest func
function loadXMLDoc (url)
{
  if (window.XMLHttpRequest) {
    req = new XMLHttpRequest ();
    req.onreadystatechange = processReqChange;
    req.open ("GET", url, true);
    req.send (null);
  } else if (window.ActiveXObject) {
    req = new ActiveXObject ("Microsoft.XMLHTTP");
    if (req) {
      req.onreadystatechange = processReqChange;
      req.open ("GET", url, true);
      req.send ();
    }
  }
}