/** The document frequency field. */
    public static final String DOC_FREQ = "docFreq";
    /** The user boost field. */
    public static final String USER_BOOST = "userBoost";
    /** The kinds field. */
    public static final String KINDS = "kinds";
    /** The timestamp field. */
    public static final String TIMESTAMP = "@timestamp";
    /** The tags field. */
    public static final String TAGS = "tags";
    /** The roles field. */

  "properties": {
    "@timestamp": {
      "type": "date",
      "format": "epoch_millis"
    },
    "docFreq": {
      "type": "long"
    },
    "fields": {
      "type": "keyword"
    },
    "kinds": {
      "type": "keyword"
    },
    "queryFreq": {
      "type": "long"
    },
    "roles": {
      "type": "keyword"
    },
    "languages": {
      "type": "keyword"
    },
    "score": {

     * @return The QueryBuilder instance.
     */
    protected QueryBuilder buildQuery() {
        final BoolQueryBuilder queryBuilder = QueryBuilders.boolQuery();
        queryBuilder.must(QueryBuilders.termQuery(FieldNames.KINDS, SuggestItem.Kind.QUERY.toString()));
        queryBuilder.mustNot(QueryBuilders.existsQuery(FieldNames.READING_PREFIX + "1"));
        queryBuilder.must(QueryBuilders.rangeQuery(FieldNames.QUERY_FREQ).gte(queryFreqThreshold));