private String extendFeature(int nnIndex, String nnWord, int jjIndex) {
        TreeMap<Integer, String> featureSet = new TreeMap<Integer, String>();
        featureSet.put(nnIndex, nnWord);
        for (TypedDependency dp : typeDP) {
            if ((dp.reln().toString() == "amod" || dp.reln().toString() == "nn")
                    && dp.gov().index() == nnIndex) {
                if (dp.dep().index() != jjIndex) {
                    featureSet.put(dp.dep().index(), dp.dep().toString());
                }
            }
        }

        String extendedFeature = "";
        for (Map.Entry<Integer, String> entry : featureSet.entrySet()) {
            extendedFeature += entry.getValue() + " ";
        }
        return extendedFeature.trim();
    }