<operator name="SparseFormatExampleSource" class="SparseFormatExampleSource">
  <parameter key="dimension"      value="1000"/>
  <parameter key="attribute_file" value="mydata.dat"/>
  <parameter key="format"         value="xy"/>
  <list key="prefix_map">
    <parameter key="w"	value="weight"/>
  </list>
</operator>
