GEXFの書き方 ref: http://qiita.com/items/42799a77faa053dc7418

attr.gexf

<?xml version="1.0" encoding="UTF-8"?>
<gexf xmlns="http://www.gexf.net/1.2draft"
      xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
      xsi:schemaLocation="http://www.gexf.net/1.2draft http://www.gexf.net/1.2draft/gexf.xsd"
      version="1.2">
  <graph defaultedgetype="directed">

    <attributes class="node">
      <attribute id="0" title="kind" type="string">
        <options>source|sink|others</options>
      </attribute>
    </attributes>
    <attributes class="edge">
      <attribute id="0" title="capacity" type="float" />
      <attribute id="1" title="flow" type="float" />
    </attributes>

    <nodes>
      <node id="0" label="Hoge">
        <attvalues>
          <attvalue for="0" value="source" />
        </attvalues>
      </node>
      <node id="1" label="Piyo">
        <attvalues>
          <attvalue for="0" value="others" />
        </attvalues>
      </node>
      <node id="2" label="Fizz">
        <attvalues>
          <attvalue for="0" value="others" />
        </attvalues>
      </node>
      <node id="3" label="Buzz">
        <attvalues>
          <attvalue for="0" value="sink" />
        </attvalues>
      </node>
    </nodes>

    <edges>
      <edge id="0" source="0" target="1">
        <attvalues>
          <attvalue for="0" value="2.0" />
          <attvalue for="1" value="1.0" />
        </attvalues>
      </edge>
      <edge id="1" source="1" target="2">
        <attvalues>
          <attvalue for="0" value="1.0" />
          <attvalue for="1" value="0.0" />
        </attvalues>
      </edge>
      <edge id="2" source="1" target="3">
        <attvalues>
          <attvalue for="0" value="1.0" />
          <attvalue for="1" value="1.0" />
        </attvalues>
      </edge>
    </edges>
  </graph>
</gexf>

hello.gexf

<?xml version="1.0" encoding="UTF-8"?>
<gexf xmlns="http://www.gexf.net/1.2draft"
      xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
      xsi:schemaLocation="http://www.gexf.net/1.2draft
                          http://www.gexf.net/1.2draft/gexf.xsd"
      version="1.2">
  <graph defaultedgetype="directed">
    <nodes>
      <node id="0" label="Hoge" />
      <node id="1" label="Piyo" />
      <node id="2" label="Fizz" />
      <node id="3" label="Buzz" />
    </nodes>
    <edges>
      <edge id="0" source="0" target="1" />
      <edge id="1" source="1" target="2" />
      <edge id="2" source="1" target="3" />
    </edges>
  </graph>
</gexf>