Defeasible Rules in Content Selection and Text Structuring

This paper outlines a number of ways in which defeasible rules can contribute to the content selection and discourse structuring components of a text generation system. We suggest that, for certain types of descriptive text, the characterisation of discourse structuring mechanisms as operations on or involving defeasible rules provides an attractive framework for addressing important issues in content selection/structuring. We describe an architecture which incorporates defeasible rules into a systemic model of generation, and illustrate its use in the description of objects in a museum gallery.
While defeasible rules are traditionally used in theorem proving applications, to make predictions about the consequences of known facts, we are here concerned with three separate issues: (i) how such rules may need to be expressed by the NLG system in order to achieve its goals; (ii) how their interaction with facts about particular objects enables the use of valuable coherence relations; and (iii) how they are relevant in taking account of the system's user model.