Evaluating plan recognition systems: Three properties of a good explanation

Plan recognition in a dialogue system is the process of explaining why an utterance was made, in terms of the plans and goals that its speaker was pursuing in making the utterance. I present a theory of how such an explanation of an utterance may be judged as to its merits as an explanation. I propose three criteria for making such judgments: applicability, grounding, and completeness. The first criterion is the applicability of the explanation to the needs of the system that will use it. The second criterion is the grounding of the explanation in what is already known of the speaker and of the dialogue. Finally, the third criterion is the completeness of the explanation's coverage of the goals that motivated the production of the utterance. An explanation of an utterance is a good explanation of that utterance to the extent that it meets these three criteria. In addition to forming the basis of a method for evaluating the merit of an explanation, these criteria are useful in designing and evaluating a plan recognition algorithm and its associated knowledge base.