EDIT

        <field>

          <!-- not fully correct to only use the first node, needs custom converter to implement correctly -->

          <a>taxonNodes[0].childNodes</a>

          <b>hasRelationship</b>

          <a-hint>eu.etaxonomy.cdm.model.taxon.TaxonNode</a-hint>

          <b-hint>eu.etaxonomy.cdm.remote.dto.tdwg.voc.Relationship</b-hint>

        </field>

    <mapping> 

        <class-a>eu.etaxonomy.cdm.model.taxon.TaxonNode</class-a>

        <class-b>eu.etaxonomy.cdm.remote.dto.tdwg.voc.Relationship</class-b>

       <field>

           <a>taxon</a>

           <b>fromTaxon</b>

       </field>

       <field>

         <a>parent.taxon</a>

         <b>toTaxon</b>

       </field>

       <field custom-converter-param="taxIncluded" type="one-way" custom-converter-id="constantConverter">

          <a>this</a>

          <b>relationshipCategory</b>

       </field>

       <field-exclude>

           <a>createdBy.username</a>

           <b>creator</b>

       </field-exclude>

       <field-exclude>

           <a>updatedBy.username</a>

           <b>contributor</b>

       </field-exclude>

</mapping>