Browsing by Author "Gurney, John"
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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 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)