Browsing by Author "Purang, Khemdut"
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Item Active Logic and Heim's Rules for Updating Discourse Context(1998-10-15) Gurney, John; Perlis, Don; Purang, KhemdutDiscourse unfolds in time, giving rise to a cascade of belief changes in the listener. Yet this temporal evolution of discourse and belief is typically ignored in theoretical treatments of discourse. It has been claimed (see Soames~\cite{soames:presuppositions}) that Heim's~\cite{heim:projection_problem} theory of discourse context accounts for non-implicative discourse updating. We will present a new non-implicative discourse that cannot be accounted for with Heim's use of global or local accommodation and which appears to require attention to \emph{evolution} of discourse. We use this example to motivate remaking Heim's update function, aimed toward a unified approach to discourse---one in which Heim's rules for discourse updating can account for more of the problem cases for the theory of discourse context. These rules and the revised update function can then serve as principles that constrain the building of representations for discourse context (such as the Discourse Representation Structures, of Discourse Representation Theory, ~\cite{kamp:reyle}). We propose \emph{active logic} as a convenient tool for executing the required inferences (as called for by our revised version of Heim's update function) as the discourse evolves through time. (Also cross-referenced as UMIACS-TR-96-43)Item Active Logic Applied to Cancellation of Gricean Implicture(1998-10-15) Purang, Khemdut; Perlis, Don; Gurney, JohnDialog proceeds over time, during which inferred beliefs come and go in the listener. Yet this temporal aspect of dialog and belief is typically ignored in theoretical treatments of dialog. Using a simple example of a dialog with an implicature that arises partway through and then is later retracted, we discuss how Gricean maxims and nonmonotonicity may relate to each other and to a computational treatment of implicature. In effect we seek to track reasoning along Gricean lines over time. We present our own computational approach to this, giving an implementation in the formalism of active logics. (Also cross-referenced as UMIACS-TR-96-42)Item Conversational Adequacy: Mistakes are the Essence(1998-10-15) Perlis, Don; Purang, KhemdutWe 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 base 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 that there may be a core set of meta-dialog principles that is in some sense complete. 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. (Also cross-referenced as UMIACS-TR-96-41)Item Defaults Denied(1998-10-15) Miller, Michael; Perlis, Don; Purang, KhemdutWe take a tour of various themes in default reasoning, examining new ideas as well as those of Brachman, Delgrande, Poole, and Schlechta. An underlying issue is that of stating that a potential default principle is not appropriate. We see this arise most dramatically as a problem in an attempt to formalize what are often loosely called "prototypes", although it also arises in other formal approaches to default reasoning. Some formalisms in the literature provide solutions but not without costs. We propose a formalism that appears to avoid these costs; it can be seen as a step toward a population-based set-theoretic modification of these approaches, that may ultimately provide a closer tie to recent work on statistical (quantitative) foundations of (qualitative) defaults([1]). Our analysis in particular indicates the need to resolve a conflation between use and mention in many default formalisms. Our treatment proposes such a resolution, and also explores the use of sets toward a more population-based notion of default. (Also cross-referenced as UMIACS-TR-96-61)Item Updating Discourse Context with Active Logic(1998-10-15) Gurney, John; Purang, Khemdut; Perlis, DonIn this paper we present our implementation of a system of active logic that processes natural language discourses. We focus on problems that involve presupposition and the associated well-known problems of the projection of presupposition. We discuss Heim's largely successful theory of presupposition and point out certain limitations. We then use these observations to build our discourse processor based on active logic. Our main contributions are the handling of problems that go beyond the scope of Heim's theory , especially discourses the involve cancellation of presupposition. Ongoing work suggests that conversational implicature and the cancellation of implicature can also be treated by our methods. Key words: presupposition, discourse, con text, accommodation, active logic, implicature. (Also cross-referenced as UMIACS-TR-96-62)