A type theoretic approach to information state update in issue based
			 dialogue management

			     Robin Cooper
			 Göteborg University

For several years the research group at our Dialogue Systems Lab has
been involved in the development of the information state update
approach to the building of dialogue systems and in particular Issue
based dialogue management developed in Staffan Larsson's PhD thesis
and based on Jonathan Ginzburg's gameboard approach to dialogue,
focussing on the notion of questions (or issues) under discussion.
Larsson's computational approach to information state updates involves
a large collection of update rules which fire when certain conditions
in the information state are met in a regime determined by a general
control algorithm.  An utterance by a dialogue participant will in
general unleash a whole chain of such updates and part of the power of
the approach lies in the fact that we can define very general update
rules which have small effects on the information state and which are
not necessarily linked to any particular form of utterance.  It gives
us a much finer grain on update rules than thinking in terms of single
monolithic updates associated with speaker utterances.

Larsson's formulation of update rules is based on a Prolog
implementation and exploits some aspects of Prolog:  logic programming
variables, backtracking to deal with non-determinism, ordering of
update actions within an update rule.  In this paper we will show how
notions of record and record type in type theory can be used to formulate
update rules without relying on these aspects of Prolog.  This allows
us to give an abstract characterisation of update rules independent of
programming language which points to a general theory of updates as well
as the possibility of implementation in any programming language. The
tools we are using can also be used in an account of compositional
semantics and this points to the possibility of an integrated formal theory
of information state update and compositional semantics.  

This work is related to other work on computational approaches to
information state update by Johan Bos on the Dipper system and to type
theoretical approaches to semantics and dialogue which exploit the
notion of context in type theory, e.g. work by Ranta, Ahn et al. and
Piwek.