This q u e s t i o n is particularly important for the construction of cooperative dialo 9 systems, since, i n many a p p l i cations, no e x p l i c i t knowledge about the dialog goals of the questioner is available at the outset. If a,system is nevertheless expected to 'over-answer , . to volunteer information that has n o t s p e c i f i c a l l y been r e q u e s t e d , it must command a s e t.