Discourse Processing of Dialogues with Multiple Threads

Discourse Processing of Dialogues with Multiple Threads Carolyn Penstein Ros~ t, Barbara Di Eugenio t, Lori S. Levin t, Carol Van Ess-Dykema t t Computational Linguistics Program Carnegie Mellon University Pittsburgh, PA, 15213 {cprose, dieugeni}@icl, cmu. edu Isl©cs. cmu. edu * Department of Defense Mail stop: R525 9800 Savage Road Ft. George G. Meade, MD 20755-6000 cj vanes©afterlife, ncsc. mil Abstract In this paper we will present our ongoing work on a plan-based discourse processor developed in the context of the Enthusiast Spanish to English translation system as part of the JANUS multi-lingual speech-to- speech translation system. We will demon- strate that theories of discourse which pos- tulate a strict tree structure of discourse on either the intentional or attentional level are not totally adequate for handling spontaneous dialogues. We will present our extension to this approach along with its implementation in our plan-based dis- course processor. We will demonstrate that the implementation of our approach out- performs an implementation based on the strict tree structure approach. 1 Introduction In this paper we will present our ongoing work on a plan-based discourse processor developed in the con- text of the Enthusiast Spanish to English translation system (Suhm et al. 1994) as part of the JANUS multi-lingual speech-to-speech translation system. The focus of the work reported here has been to draw upon techniques developed recently in the compu- tational discourse processing community (Lambert 1994; Lambert 1993; Hinkelman 1990), developing a discourse processor flexible enough to cover a large corpus of spontaneous dialogues in which two speak- ers attempt to schedule a meeting. There are two main contributions of the work we will discuss in this paper. From a theoretical stand- point, we will demonstrate that theories which pos- tulate a strict tree structure of discourse (henceforth, Tree Structure Theory, or TST) on either the inten- tional level or the attentional level (Grosz and Sidner 1986) are not totally adequate for covering sponta- neous dialogues, particularly negotiation dialogues which are composed of multiple threads. These are negotiation dialogues in which multiple propo- sitions are negotiated in parallel. We will discuss our proposea extension to TST which handles these structures in a perspicuous manner. From a prac- tical standpoint, our second contribution will be a description of our implemented discourse processor which makes use of this extension of TST, taking as input the imperfect result of parsing these sponta- neous dialogues. We will also present a comparison of the perfor- mance of two versions of our discourse processor, one based on strict TST, and one with our extended version of TST, demonstrating that our extension of TST yields an improvement in performance on spontaneous scheduling dialogues. A strength of our discourse processor is that because it was designed to take a language- independent meaning representation (interlingua) as its input, it runs without modification on either En- glish or Spanish input. Development of our dis- course processor was based on a corpus of 20 spon- taneous Spanish scheduling dialogues containing a total of 630 …

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