<!-- Is el1 primary key always mapped in the top of the column list? -->
<dataset_root>

<el1 attr1='val1' attrA='valA'>
  <X />
  <el2 attr2='val2' attrB='valB'>
    <el3 attr3='val3' attrC='valC'>3</el3>
      <column2>1</column2>
      <column3>1</column3>
    <el4 attr4='val4' attrD='valD'>4</el4>
  </el2>
  <Y />
</el1>
<el1 attrExt='ext' />

</dataset_root>

