<esri:ClassBreaksRenderer attribute="ranking">
     <esri:ClassBreakInfo maxValue="0.33" symbol="{smallSym}"/>
     <esri:ClassBreakInfo minValue="0.33" maxValue="0.67" symbol="{mediumSym}"/>
     <esri:ClassBreakInfo minValue="0.67" symbol="{largeSym}"/>
 </esri:ClassBreaksRenderer>

var smallSym:SimpleMarkerSymbol = new SimpleMarkerSymbol(SimpleMarkerSymbol.STYLE_CIRCLE,6, 0xFF0000, 0.7);
var mediumSym:SimpleMarkerSymbol = new SimpleMarkerSymbol(SimpleMarkerSymbol.STYLE_CIRCLE,10, 0xFF0000, 0.7);
var largeSym:SimpleMarkerSymbol = new SimpleMarkerSymbol(SimpleMarkerSymbol.STYLE_CIRCLE,16, 0xFF0000, 0.7);

var classBreaksRenderer:ClassBreaksRenderer = new ClassBreaksRenderer();
classBreaksRenderer.attribute = "BUILD_DATE";
var classBreakInfos:Array = [
    new ClassBreakInfo(smallSym, Number.NEGATIVE_INFINITY, 1980),
    new ClassBreakInfo(mediumSym, 1980, 2000),
    new ClassBreakInfo(largeSym, 2000, Number.POSITIVE_INFINITY)
];

classBreaksRenderer.infos = classBreakInfos;
graphicsLayer.renderer = classBreaksRenderer;