public void initialize(Configuration conf, Properties tbl) throws TException {
    sortOrder = tbl.getProperty(serdeConstants.SERIALIZATION_SORT_ORDER);
    if (sortOrder == null) {
      sortOrder = "";
    }
    for (int i = 0; i < sortOrder.length(); i++) {
      char c = sortOrder.charAt(i);
      if (c != '+' && c != '-') {
        throw new TException(serdeConstants.SERIALIZATION_SORT_ORDER
            + " should be a string consists of only '+' and '-'!");
      }
    }
    LOG.info("Sort order is \"" + sortOrder + "\"");
  }
Whether the current field is sorted ascendingly. Always equals to
sortOrder.charAt(topLevelStructFieldID) != '-'
serde/src/java/org/apache/hadoop/hive/serde2/thrift/TBinarySortableProtocol.java