code: private static String mapEnglishPennTagSetToNAF(final String postag) {
      if (postag.startsWith("RB")) {
        return "A"; // adverb
      } else if (postag.equalsIgnoreCase("CC")) {
        return "C"; // conjunction
      } else if (postag.startsWith("D") || postag.equalsIgnoreCase("PDT")) {
        return "D"; // determiner and predeterminer
      } else if (postag.startsWith("J")) {
        return "G"; // adjective
      } else if (postag.equalsIgnoreCase("NN")
          || postag.equalsIgnoreCase("NNS")) {
        return "N"; // common noun
      } else if (postag.startsWith("NNP")) {
        return "R"; // proper noun
      } else if (postag.equalsIgnoreCase("TO") || postag.equalsIgnoreCase("IN")) {
        return "P"; // preposition
      } else if (postag.startsWith("PRP") || postag.startsWith("WP")) {
        return "Q"; // pronoun
      } else if (postag.startsWith("V")) {
        return "V"; // verb
      } else {
        return "O"; // other
      }
    }
docs: Mapping between Penn Treebank tagset and NAF tagset.
  
  @param postag
  treebank postag
  @return NAF POS tag