Symbol Definition xi or yi a token in the dialog history or system response $ a special token used as a sentinel <cite>(Madotto et al., 2018 )</cite> X X = {x1, . . . , xn, $}, the dialog history Y Y = {y1, · · · , ym}, the expected response bi one KB tuple, actually the corresponding entity B B = {b1, · · · , b l , $}, the KB tuples P T RE = {ptrE,1, · · · , ptrE,m}, dialog pointer index set.