XML : get values out of xml file for barchart

I have a xml like this:

  <chart showValues="0" adjustDiv="0" showLabels="1" rotateLabels="1" slantLabels="1" xAxisName="" yAxisMinValue="-1" yAxisMaxValue="2" showYAxisValues="0" numDivLines="0" zeroPlaneAlpha="0" plotSpacePercent="10" plotFillRatio="100" caption="" labelStep="4" numVDivLines="15" vDivLineAlpha="10" animation="1" bgColor="FFFFFF" bgAlpha="0" showBorder="0" borderColor="415D6F" borderThickness="1" canvasBgColor="FFFFFF" canvasBgAlpha="100" canvasBorderColor="545454" canvasBorderAlpha="100" canvasBorderThickness="1" showCanvasBase="1" chartTopMargin="" chartLeftMargin="" chartRightMargin="" chartBottomMargin="-5" labelPadding="5" yAxisValuesPadding="7" hoverCapBgColor="ffffff" hoverCapBorderColor="708290" baseFont="Tahoma" baseFontSize="11" baseFontColor="535454" divLineColor="FFFFFF" divLineAlpha="65" divLineThickness="1" showAlternateHGridColor="0" alternateHGridColor="92CDD6" alternateHGridAlpha="10" legendBgColor="FFFFFF" legendBgAlpha="0" legendBorderColor="415D6F" legendBorderAlpha="50" legendBorderThickness="1" legendShadow="0" legendScrollBgColor="CCCCCC" legendScrollBarColor="CCCCCC" legendScrollBtnColor="999999" useRoundEdges="1">      <categories>      <category label="00:00"/>      <category label="01:00"/>      <category label="02:00"/>      </categories>      <dataset>      <set value="2" color="8BBA00" alpha="100" toolText="Jan 12 24:00, Normal"/>      <set value="1" color="8BBA00" alpha="100" toolText="Jan 12 01:00, Warning"/>      <set value="1" color="8BBA00" alpha="100" toolText="Jan 12 02:00, Warning"/>      </dataset>      </chart>    

how can I get the "value" out of it? I need the value for a barchart. I think getElementsByTagName() is not working in ths context?