Using Linguistic, World, and Contextual Knowledge in a Plan Recognition Model of Dialogue

USING LINGUISTIC, WORLD, AND CONTEXTUAL KNOWLEDGE IN A PLAN RECOGNITION MODEL OF DIALOGUE ~ LYNN LAMBERT and SANDRA CARBERRY Department of Computer and Information Sciences University of Delaware Newark, Delaware 19716, USA email : lambert@cia, udel, edu, earberry@cis, udel, edu Abstract This paper presents a plan-based model of dialogue that combines world, linguistic, and contextual knowl- edge in order to recognize complex communicative ac- tions such as expressing doubt. Linguistic knowledge suggests certain discourse acts, a speaker's beliefs, aud the strength of those beliefs; contextual knowledge sug- gests the most coherent continuation of the dialogue; and world knowledge provides evidence that the appli- cability conditions hold for those discourse acts that capture the relationship of the current utterance to the discourse as a whole. 1 Introduction Recognizing the roles that utterances play in a dialogue and how the utterances should be interpreted in the context of preceding dialogue is a crucial part of a robust model of understanding. In order to perform this recognition, our tripartite plan-based model of di- alogue identifies not only domain and problem-solving actions but also discourse or communicative actions that determine how utterances relate to each other. For this communicative action recognition, we com- bine information gleaned from a variety of knowledge sources: contextual, linguistic, and world knowledge. The combination of these different knowledge sources enables the recognition of complex communicative ac- tions such as expressing donbt. Although our tripar- tite model recognizes three different kinds of actions (domain, problem-solving, and discourse), the focus of this paper will be the recognition of discourse actions and how a combination of knowledge sonrces enables us to perform this recognition. 2 Our Tripartite Model A number of researchers have contended that a coherent discourse consists of segments that are related to one another through some type of structuring rela- tion [Gri75, MT83] or have modeled discourse based on the semantic relationship of individual clauses [Pol86] or groups of clauses [Rei78]. But all of these fail to capture the goal-oriented natnre of discoursc. Grosz and Sidner [GS86] argue that recognizing the struc- tural relationships among the intentions underlying a 1 This work is being supported by the National Science Foun- dation trader Graait No. IR1-9122026. The ~overrlnlellt h&s cer- tMn rights in tiffs material. discourse is necessary to identify discourse structure; although they do not provide the details of a compu- tational mechanism for recognizing these relationships, they do argue convincingly that it requires multiple knowledge sources. We have developed a plan-based model of dialogue and have incorporated into our model Grosz and Sidner's claim that linguistic, contextual, and world knowledge should be combined in recogniz- ing the role of an utterance in a discourse. . We contend that at least three kinds of ac- tions, domain, problem-solving, and discourse, should be captured by a model of task-oriented dialogue. Many researchers [A1179, Car87, LAB7, Sid85, GS86] have demonstrated that recognition of domain ac- tions endows a system with the ability to success- fnlly address many important and difficult problems …

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