code: protected final String getTaxonomy(final Element desc) {
          String taxonomy = null;
          final Element topic = desc.getChild("topic", getTaxonomyNamespace());
          if (topic != null) {
              final Attribute resource = topic.getAttribute("resource", getRDFNamespace());
              if (resource != null) {
                  taxonomy = resource.getValue();
              }
          }
          return taxonomy;
      }
docs: Utility method to parse a taxonomy from an element.
  <p>
  
  @param desc the taxonomy description element.
  @return the string contained in the resource of the element.