method register_name s role_id =
if (Hashtbl.mem string_to_id (s,role_id)) then
Hashtbl.find string_to_id (s,role_id)
else
let string_id = ident_number in
(Hashtbl.add string_to_id (s,role_id) string_id ;
Hashtbl.add id_to_string string_id s;
ident_number <- ident_number+1;
string_id)