code: @Override
      public String getPreferredPrefix(String namespaceUri, String suggestion, boolean requirePrefix) {
          if ((defaultNamespace!=null) && (namespaceUri.equals(defaultNamespace))) {
              return "";
          }
  
          if (namespaceUri.equals(PROV_NS)) {
              return "prov";
          }
          if (namespaceUri.equals(PRINTER_NS)) {
              return "prn";
          }
     //     if (namespaceUri.equals(XSD_NS)) {
     //         return "xsd";
     //     }
          if (namespaceUri.equals(DOMProcessing.XSD_NS_FOR_XML)) { // TODO: TO CHECK that's the one we need
              return "xsd";
          }
          if (namespaceUri.equals(XML_NS)) {
              return "xml";
          }
          if (namespaceUri.equals(XSI_NS)) {
              return "xsi";
          }
          for (String k: nss.keySet()) {
              if (nss.get(k).equals(namespaceUri)) {
                  return k;
              }
          }
          return suggestion;
      }
docs: /* (non-Javadoc)
  @see org.openprovenance.prov.model.NamespacePrefixMapper#getPreferredPrefix(java.lang.String, java.lang.String, boolean)