var $ = go.GraphObject.make;
       myDiagram = $(go.Diagram, "myDiagramDiv");
       var nodeDataArray = [
           { key: "Alpha", color: "lime" },
           { key: "Beta", color: "cyan" },
           { key: "Zeta", isGroup: true },
           { key: "Delta", color: "pink", group: "Zeta" },
           { key: "Gamma", color: "maroon", group: "Zeta" }
       ];
       var linkDataArray = [
           { to: "Beta", from: "Alpha", color: "red" },
           { to: "Zeta", from: "Alpha" }
       ];
       myDiagram.model = new go.GraphLinksModel(nodeDataArray, linkDataArray);

       myDiagram.nodeTemplate =
       $(go.Node, "Auto",
           $(go.Shape, "RoundedRectangle", { fill: "white", },
               new go.Binding("fill", "color")
           ),
           $(go.TextBlock, "text", { margin: 10 },
               new go.Binding("text", "key")
           )
       );

       myDiagram.linkTemplate =
       $(go.Link,
           $(go.Shape, { strokeWidth: 3 },
               new go.Binding("stroke", "color")),
           $(go.Shape,
           { toArrow: "Standard", stroke: null },
               new go.Binding("fill", "color"))
       );