public byte[] getGraph(String dot_source, String type)
   {
      File dot;
      byte[] img_stream = null;
   
      try {
         dot = writeDotSourceToFile(dot_source);
         if (dot != null)
         {
            img_stream = get_img_stream(dot, type);
            if (dot.delete() == false) 
               System.err.println("Warning: " + dot.getAbsolutePath() + " could not be deleted!");
            return img_stream;
         }
         return null;
      } catch (java.io.IOException ioe) { return null; }
   }