Integrating Qualitative Reasoning And Text Planning To Generate Casual Explanations

Several works IMcKeowu 86, Suthers 88] have emphasized the common aspects of Explanation Production in expert systems and Text Generation. The work described in this paper deals with text generation applied to a particular type of explanations: causal explanations of physical systems. They have akeady motivated influential developments in the field of qualitative reasoning about physical systems. A central goal of the theories developed in [De Kleer 84] and [Forbus 84] was to elaborate conceptual frameworks for providing causal accounts of physical systems , sensitive to our commonsense understanding of the physical world. Those qualitative causal models constitute an adequate starting point as we are interested in how people present such causal explanations in verbal form. We will describe our approach for text generation, based ou the study of texts collected in encyclopedia and textbooks, and currently developed in a system intended to be associated to the qualitative simulation system SQUALE [J6z6quel & Zimmer 92]. Our conceptual model, which constitutes the input to the text generation process, is based on Qualitative Process Theory IForbus 84]. According to the "traditional" division of tasks in text generation, the transition from conceptual representation of causal behaviour to causal explanation in natural lau-gouge is viewed as a three-stage process: content specification , text organization and surface generation. The content specification task aims at posting communicative goals described by means of communicative acts on conceptual entities. In particular, the causal explanation to be produced is often restricted to ,some particular events of the causal behaviour. We will show how relevant information and appropriate communicative acts are identified. Text organization is the most elaborate part of our model and is also divided into three tasks. The first is concerned with the construction of a textual structure from a set of communicative acts established during content specification. This structure, which takes an intermediary place between communicative acts and surface realizations, specifies essentially prescriptions on grouping and ordering of textual units. This process is achieved through the application of discourse strategies which control local Iransitions from communicative acts to possible organizational preseriptions. We dcseribe three strategies used for structuring causal explanations: a causal chain strategy (for organizing simple causal chains), a parallel strategy (to impose a parallel structure on the text), and a concessive strategy (for performing concessive acts). The second task segments the textual structure into sentential contents. Several factors are revolved, mainly communicative form of textual …