module MessageBoard {

 struct Message_info
 {
   string message_id;
   string message_title;
   string message_originator;
   long long message_create_time; 
 };

 exception does_not_exist
 {
    string reason;
 };

 exception not_allowed
 {
    string reason;
 };

 interface Message   // to read info from a message
 {    
   string get_message_id();
       
   string get_text();
    
   string get_title();
    
   string get_message_originator(); 
    
   long long get_message_create_time(); 
 };

 interface Board // to post, read and remove messages on the board
 {  
   void post_message(in string title , in string text);

   Message get_message(in string message_id) raises(does_not_exist);
    
   void remove_message(in string message_id) raises(not_allowed,does_not_exist);
    
   void set_init_message_info();                          // This operation creates a copy of all message titles on the server that
                                                          // then can be retrieved by successive "get_next_message_info()" operations. 
    
   Message_info get_next_message_info() raises(does_not_exist); // By successive calls to this operation all message titles on the server 
                                                                // can be retrieved. Before "set_init_message_info()" must be called.
                                                                // When there are no more message titles exception "does_not_exist" will be raised.
 };

 interface BoardCallback   // this interface is used by the server to inform the clients about a change on the board.
                           //  After receiving this the client should perform a new message title reading from the server as above)
 {
   void board_changed(); 
 };  

 interface BoardConnect    // Interface to the login object. A reference to this is given in the ior-string.       
 {
   Board login(in string user, in string passwd, in BoardCallback call_back)  raises(does_not_exist, not_allowed); // Client login.
                                                                                                                   // It is allowed to give null value for "call_back",                                                                                               //  then there will be no callback from the server.
 };
};