2 This is precisely the consideration on which the initial work on referring expression generation was based, inspired by Grosz and Sidner's (1986) observations about how the changing attentional structure of a discourse moves different entities in and out of focus.
in addition to the main prediction class content pattern, the split was stratified for Speaker iD and Quartile to ensure that training and test set contained the same proportion of descriptions from each speaker and each quartile of the dialogues.