Implementing a Normative Theory of Communication in a Framework for Default Reasoning

This thesis presents a framework for inter-agent communication, represented and partially implemented with default reasoning. I focus on the limited goal of determining the meaning for a Hearer-agent of an utterance $\omega$ by a Speaker-agent, in terms of the beliefs of the interlocutors. This meaning is generally more than just the explicit propositional contents of $\omega$, and more than just the Speaker's goal to convey her belief that $\omega$. One way of determining this meaning is to let the Hearer take stock of the implicit components of the Speaker's utterances. Among the implicit components of the meaning of $\omega$, I show in particular how to derive certain of its presuppositions with a set of default schemata using a framework for default reasoning. More information can be extracted from the communications channel between interlocutors by adopting a normative model of inter-agent communication, and using this model to explain or 'make sense' of the Speaker's utterances. I construct such a model expressed in terms of a set of default principles of communication using the same framework for default reasoning. The task of deriving the meaning of an utterance is similar to the job required of a user-interface, where the user is the Speaker-agent, and the interface itself is the Hearer-agent. The goal of a user-interface as Hearer is to make maximal use of the data moving along the communications channel between user and application. The result is an integrated theory of normative, inter-agent communications expressed within an ontologically and logically minimal framework. This work demonstrates the development and application of a methodology for the use of default reasoning. The implementation of the theory is also presented, along with a discussion of its applicability to practical user-interfacing. A view emerges of user-modelling as a component of a user-interface.