article = focus = theme
                           /-  FOCUS = THEME
                         /-     
                       /-
                     /-    
                   /-   (members can create/change 
                 /-      relation after publishing)
               /-
           article

             /|\ PARENT
              |        
              |      (create parent-child relation 
              |       by using "Reply" function)
              | 
             \|/ CHILD 

        comment = reply



"message" means any article or comment or focus