This paper contains a description of Traum’s Grounding Acts model. He developed this model to address some of the specific deficienses of Clark and Schaefer’s Contribution Model. Particularly, he critics their model because: a) it is not clear that contributions are ever really complete; b) there is no graded evidence of understanding; c) it is difficult to define the initiation of the next relevant contribution; d) it is hard to tell whether a particular utterance is part of the presentation phase or the acceptance phase; e) there is no easy way to tell the “state”of the current contribution while engaged in a conversation. He states that this model is of no use for collaborative systems, and therefore he develops the Grounding Acts model, which collapses the different types of acceptance and extends the building blocks of the units of common ground to those that could be realised with a single utterance thus allowing an agent to track progress of each communication without lookahead.
He defines Discourse Units (DU), rather than Contributions; and Grounding Acts, as the basic building blocks. Each of these is identified with a particular utterance unit and performs a specific function toward the achievement of the common ground.
In the same paper he defines the deficiencies of his own model as: a) the oversimplification of the “grounded or not grounded” distinction; b) the dependancy of the model on the size of the utterance units; c) the difficulty in recognising which act was performed; d) the in-sensitivities to modalities other than spoken language.