code: private static String mapGermanCoNLL09TagSetToNAF(final String postag) {
      if (postag.startsWith("ADV")) {
        return "A"; // adverb
      } else if (postag.startsWith("KO")) {
        return "C"; // conjunction
      } else if (postag.equalsIgnoreCase("ART")) {
        return "D"; // determiner and predeterminer
      } else if (postag.startsWith("ADJ")) {
        return "G"; // adjective
      } else if (postag.equalsIgnoreCase("NN")) {
        return "N"; // common noun
      } else if (postag.startsWith("NE")) {
        return "R"; // proper noun
      } else if (postag.startsWith("AP")) {
        return "P"; // preposition
      } else if (postag.startsWith("PD") || postag.startsWith("PI")
          || postag.startsWith("PP") || postag.startsWith("PR")
          || postag.startsWith("PW") || postag.startsWith("PA")) {
        return "Q"; // pronoun
      } else if (postag.startsWith("V")) {
        return "V"; // verb
      } else {
        return "O"; // other
      }
    }
docs: Mapping between CoNLL 2009 German tagset and NAF tagset. Based on the
  Stuttgart-Tuebingen tagset.
  
  @param postag
  the postag
  @return NAF POS tag