| dc.description.abstract | The goal of this research is to develop explanation presentation mechanisms for knowledge based
systems which enable them to define domain terminology and concepts, narrate events, elucidate plans,
processes, or propositions and argue to support a claim or advocate action. This requires the development
of devices which select, structure, order and then linguistically realize explanation content as coherent and
cohesive English text.
With the goal of identifying generic explanation presentation strategies, a wide range of naturally
occurring texts were analyzed with respect to their communicative sttucture, function, content and intended
effects on the reader. This motivated an integrated theory of communicative acts which characterizes text at
the level of rhetorical acts (e.g., describe, define, narrate), illocutionary acts (e.g., inform, request), and
locutionary acts (e.g., ask, command). Taken as a whole, the identified communicative acts characterize
the structure, content and intended effects of four types of text: description, narration, exposition,
argument. These text types have distinct effects such as getting the reader to know about entities, to know
about events, to understand plans, processes, or propositions, or to believe propositions or want to
perform actions. In addition to identifying the communicative function and effect of text at multiple levels
of abstraction, this dissertation details a tripartite theory of focus of attention (discourse focus, temporal
focus, and spatial focus) which constrains the planning and linguistic realization of text.
To test the integrated theory of communicative acts and tripartite theory of focus of attention, a text
generation system TEXPLAN (Textual EXplanation PLANner) was implemented that plans and
linguistically realizes multisentential and multiparagraph explanations from knowledge based systems. The
communicative acts identified during text analysis were formalized as over sixty compositional and (in
some cases) recursive plan operators in the library of a hierarchical planner. Discourse, temporal, and
spatial focus models were implemented to track and use attentional information to guide the organization
and realization of text. Because the plan operators distinguish between the communicative function (e.g.,
argue for a proposition) and the expected effect (e.g., the reader believes the proposition) of communicative
acts, the system is able to construct a discourse model of the structure and function of its textual responses
as well as a user model of the expected effects of its responses on the reader's knowledge, beliefs, and
desires. The system uses both the discourse model and user model to guide subsequent utterances. To test
its generality, the system was interfaced to a variety of domain applications including a neuropsychological
diagnosis system, a mission planning system, and a knowledge based mission simulator. The system
produces descriptions, narrations, expositions, and arguments from these applications, thus exhibiting a
broader range of rhetorical coverage than previous text generation systems. | |
