LINGUIST List 14.292

Tue Jan 28 2003

Diss: Discourse Analysis: Schlangen "A Coherence..."

Editor for this issue: Karolina Owczarzak <karolinalinguistlist.org>

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1. das, Discourse Analysis: Schlangen "A Coherence-Based Approach..."

New Dissertation Abstract

Institution: University of Edinburgh
Program: School of Informatics
Dissertation Status: In Progress

Author: David Schlangen 

Dissertation Title: 
A Coherence-Based Approach to the Interpretation of Non-Sentential
Utterances in Dialogue

Linguistic Field: 
Discourse Analysis, Semantics, Pragmatics, Computational Linguistics


Dissertation Director 1: Alex Lascarides
Dissertation Director 2: Claire Grover


Dissertation Abstract: 

This thesis is concerned with a certain kind of non-sentential
utterance occuring in dialogue, namely one where the utterance,
despite its 'incomplete' syntactic form, is intended to convey a
proposition, a question or a request. Perhaps the most prominent type
of such utterance is the 'short answer', as in 'A: Who came to the
party? - B: Peter.', but there are many other types as well, as we
show.

Clearly, the interpretation of such 'fragments', as we call this kind
of non-sentential utterance, is highly context dependent. We provide
evidence that there are complex syntactic, semantic and pragmatic
constraints governing the use of fragments. In particular, following
(Ginzburg 1998), we present evidence that while the main resolution
must be semantic, some limited syntactic information nevertheless has
to persist beyond the boundaries of sentences to allow for the
formulation of certain constraints on fragments.

We argue that consequently only a theory that has at its disposal a
wide array of information sources - from syntax through compositional
and lexical semantics to domain and world knowledge, and reasoning
about cognitive states - can do justice to the complexity of their
interpretation. As we show, however, it is desirable to encapsulate
these knowledge sources as much as possible, so as to maintain
computability. Our main thesis then is that the resolution of the
intended content of fragments can be modelled as a by-product of the
establishment of 'coherence' in dialogue, which (following much of the
work on discourse) we define as the establishment of certain
connections of new material to the context. We show that all
constraints on the form and content of fragments follow from how they
are connected to the context.

It is the centrality of the notion of coherence and the feature of
having access to different kinds of information which distinguishes
our theory from prior attempts. The work of Jonathan Ginzburg and
colleagues (Ginzburg 1998, Ginzburg and Sag 2002), inter alia, for
example provides an approach to some types of fragments which is based
on unification-operations on HPSG-signs. This approach, as we will
show, fails to offer a convincing model of the interpretation of
fragments where missing content is linguistically implicit and has to
be inferred. Carberry (1990), on the other hand, employs
computationally expensive plan-recognition techniques for the
interpretion of fragments. This fails to predict certain empirical
facts and further, we will show that the complex reasoning with
cognitive states that she employs can often be replaced with much
simpler inferences based on linguistic information.

In this thesis, we offer an analysis of the syntax of fragments, of
their compositional semantics, and we provide a computational and
formally precise theory of how the compositional semantics is
supplemented with further content via reasoning about the
context - both linguistic and non-linguistic. We also describe an
implementation of our approach, based on an extension of a
wide-coverage grammar and an accompanying discourse reasoning
component for a simple domain.