code: @GET
    @Path("search/frequency")
    @Produces("application/xml")
    public FrequencyTable frequency(
      @QueryParam("q") String query,
      @QueryParam("corpora") String rawCorpusNames,
      @QueryParam("fields") String rawFields)
    {
      requiredParameter(query, "q", "AnnisQL query");
      requiredParameter(rawCorpusNames, "corpora", "comma separated list of corpus names");
      requiredParameter(rawFields, "fields", "Comma seperated list of result vector elements.");
      
      Subject user = SecurityUtils.getSubject();
      List<String> corpusNames = splitCorpusNamesFromRaw(rawCorpusNames);
      for(String c : corpusNames)
      {
        user.checkPermission("query:matrix:" + c);
      }
      
      QueryData data = queryDataFromParameters(query, rawCorpusNames);
      FrequencyTableQuery ext = FrequencyTableQuery.parse(rawFields);
      data.addExtension(ext);
      
      long start = new Date().getTime();
      FrequencyTable freqTable = queryDao.frequency(data);
      long end = new Date().getTime();
      logQuery("FREQUENCY", query, splitCorpusNamesFromRaw(rawCorpusNames), end - start);
      
      return freqTable;
    }
docs: Frequency analysis.
  
  @param  rawFields Comma seperated list of result vector elements.
  Each element has the form <node-nr>:<anno-name>. The
  annotation name can be set to "tok" to indicate that the
  span should be used instead of an annotation.