/ DOM element where the Timeline will be attached
  var container = document.getElementById('visualization');

  // Create a DataSet (allows two way data-binding)
  var items = new vis.DataSet([
    {id: 1, content: 'item 1', start: '2013-04-20'},
    {id: 2, content: 'item 2', start: '2013-04-14'},
    {id: 3, content: 'item 3', start: '2013-04-18'},
    {id: 4, content: 'item 4', start: '2013-04-16', end: '2013-04-19'},
    {id: 5, content: 'item 5', start: '2013-04-25'},
    {id: 6, content: 'item 6', st