Several such models have been proposed (Reiter and Dale, 2000;Henschel et al., 2000;Callaway and Lester, 2002;Krahmer and Theune, 2002;Gupta and Bandopadhyay, 2009;Greenbacker and McCoy, 2009).
all of these are fully deterministic, always choosing the same referential form in the same context.