We present a representation of events and action based on interval temporal logic that is significantly more expressive and more natural than most previous AI approaches. The representation is motivated by work in natural language semantics and discourse, temporal logic, and AI planning and plan recognition. The formal basis of the representation is presented in detail, from the axiomatization of time periods to the relationship between actions and events and their effects. The power of the representation is illustrated by applying it to the axiomatization and solution of several standard problems from the AI literature on action and change. An approach to the frame problem based on explanation closure is shown to be both powerful and natural when combined with our representational framework. We also discuss features of the logic that are beyond the scope of many traditional representations, and describe our approach to difficult problems such as external events and simultaneous action...

This thesis examines disfluencies (e.g., "um", repeated words, and a variety of forms of self-repair) in the spontaneous speech of adult normal speakers of American English. Despite their prevalence, disfluencies have traditionally been viewed as irregular events and have received little attention. The goal of the thesis is to provide evidence that, on the contrary, disfluencies show remarkably regular trends in a number of dimensions. These regularities have consequences for models of human language production; they can also be exploited to improve performance in speech applications. The method includes analysis of over 5000 hand-annotated disfluencies from a database (250,000 words) containing three different styles of spontaneous speech: task-oriented human-computer dialog, task-oriented human-human dialog, and human-human conversation on a prescribed topic. The approach is theory-neutral and strongly data-driven. The annotations correspond to observable characteristics ("features") ...

This paper describes the START Information Server built at the MIT Artificial Intelligence Laboratory. Available on the World Wide Web since December 1993, the START Server provides users with access to multi-media information in response to questions formulated in English. Over the last 3 years, the START Server answered hundreds of thousands of questions from users all over the world

Interactive spoken dialog provides many new challenges for spoken language systems. One of the most critical is the prevalence of speech repairs. This paper presents an algorithm that detects and corrects speech repairs based on finding the repair pattern. The repair pattern is built by finding word matches and word replacements, and identifying fragments and editing terms. Rather than using a set of prebuilt templates, we build the pattern on the fly. In a fair test, our method, when combined with a statistical model to filter possible repairs, was successful at detecting and correcting 80 % of the repairs, without using prosodic information or a parser.

We propose some domain-independent techniques for bringing well-founded partialorder planners closer to practicality. The first two techniques are aimed at improving search control while keeping overhead costs low. One is based on a simple adjustment to the default A* heuristic used by ucpop to select plans for refinement. The other is based on preferring "zero commitment" (forced) plan refinements whenever possible, and using LIFO prioritization otherwise. A more radical technique is the use of operator parameter domains to prune search. These domains are initially computed from the definitions of the operators and the initial and goal conditions, using a polynomial-time algorithm that propagates sets of constants through the operator graph, starting in the initial conditions. During planning, parameter domains can be used to prune nonviable operator instances and to remove spurious clobbering threats. In experiments based on modifications of ucpop, our improved plan and goal selecti...

Negotiation is an important part of task-oriented expert-consultation dialogues. This paper presents a plan-based model for understanding cooperative negotiation subdialogues. Our sys-tem infers both the communicative actions that people pursue when speaking and the beliefs underlying these actions. Beliefs, and the strength of these beliefs, are recognized from the surface form of utterances,from discourse acts, and from the explicit and implicit acceptance of previous utterances. Our algorithm for recognizing discourse actions combines linguistic, world, and con-textual knowledge in a unified framework. By combining these different knowledge sources, we are able to recognize complex discourse acts such as expressing doubt, to identify the relationship of utterances to one another, and to model negotiation subdialogues. Since negotiation is an inte-gral part of multiagent activity, our process model addresses an important aspect of cooperative interaction and thus is a step toward an intelligent and robust natural language consultation system.

In this paper we address the problem of scalability in temporal reasoning. In particular, new algorithms for efficiently managing large sets of relations in the Point Algebra are provided. Our representation of time is based on timegraphs, graphs partitioned into a set of chains on which the search is supported by a rnetagraph data structure. The approach is an extension of the time representation proposed by Schubert, Taugher and Miller in the context of story comprehension. The algorithms presented in this work concern the construction of a timegraph from a given set of relations and are implemented in a temporal reasoning system called TG-II. Experimental results show that our approach is very efficient, especially when the given relations admit representation as a collection of chains connected by relatively few cross-chain links. 1

Reasoning about temporal information is an important task in many areas of Artificial Intelligence. In this paper we address the problem of scalability in temporal reasoning by providing a collection of new algorithms for efficiently managing large sets of qualitative temporal relations. We focus on the class of relations forming the Point Algebra (PA-relations) and on a major extension to include binary disjunctions of PA-relations (PA-disjunctions). Such disjunctions add a great deal of expressive power, including the ability to stipulate disjointness of temporal intervals, which is important in planning applications. Our representation of time is based on timegraphs, graphs partitioned into a set of chains on which the search is supported by a metagraph data structure. The approach is an extension of the time representation proposed by Schubert, Taugher and Miller in the context of story comprehension. The algorithms herein enable construction of a timegraph from a given set of PA-r...

We consider the problem of representing plans for mixed-initiative planning, where several participants cooperate to develop plans. We claim that in such an environment, a crucial task is plan communication: the ability to suggest aspects of a plan, accept such suggestions from other agents, criticize plans, revise them, etc., in addition to building plans. The complexity of this interaction imposes significant new requirements on the representation of plans. We describe a formal model of plans based on defeasible argument systems that allows us to perform these types of reasoning. The arguments that are produced are explicit objects that can be used to provide a semantics for statements about plans.

We argue that meta-dialog and meta-reasoning, far from being of only occasional use, are the very essence of conversation and communication between agents. We give four paradigm examples of massive use of meta-dialog where only limited object dialog may be present, and use these to bolster our claim of centrality for meta-dialog. We further illustrate this with related work in active logics. We argue moreover This research has been supported in part by grants from the National Science Foundation and the Army Research Office. We thank Betsy Klipple, Tom Nelson, Clare Voss, and John Gurney for helpful discussion. y Institute for Advanced Computer Studies, University of Maryland. 1 that there may be a core set of meta-dialog principles that is in some sense complete, and that may correspond to the human ability to engage in "free-ranging" conversation. If we are right, then implementing such a set would be of considerable interest. We give examples of existing computer programs that converse inadequately according to our guidelines. 1