Sorting step that will sort according to a specified key.

<step id="alg" className="cz.adastra.cif.tasks.identify.sort.SortEngine" >
    <properties>
      <sort>
        <orderBy expression="last_name" />
        <orderBy expression="first_name" nullsFirst="true" />
        <orderBy expression="birtd_date" orderDescending="true" />
      </sort>
    </properties>
</step>