Jasper Taylor, Jean Carletta and Chris Mellish
Combining power with tractability in belief models
Belief models are used in AI computer applications
in a great many roles, both to keep track of the beliefs of users and
to simulate the belief states of agents modelled by the
system. Epistemic logic is often used as a paradigm for the behaviour
of such models, but has problems of computational complexity, which
are compounded by the need to include nonmonotonic inferences and
change over time. Systems based on standard logics also sanction
inferences which human reasoners would be unlikely to make.
In some aspects of reasoning, simplifications can be made which both
reduce the computational problems and restrict inferences to those
most plausible in humans. However, in order to reap the computational
advantages of restricting inferences, a model-building approach
similar to a compiler must be used. A description of the domain and
the agents' knowledge is entered in a formal language, and translated
into a restricted representation which allows a reasoning process
embodying the restrictions and other efficiency features to be used.
The process of compilation and execution is described in detail, and
compared with models which use different representations for different
beliefs while remaining complete in terms of standard logic.
Relationships between computational simplifications and improvements
in psychological plausibility are discussed.
(March 1996; 48 pages)
Ref. No. HCRC/RP-76 Price: UKL 1.70
Janet Hitzeman
Semantic Partition and the Ambiguity of Sentences Containing
Temporal Adverbials
The ambiguity of sentences such as (i) has been explained both in
terms of an ambiguity of the for-phrase (Dowty, 1979) and in
terms of an effect of the perfect (Kamp & Reyle, 1993):
(i) Mary has lived in Amsterdam for three years.
I argue against these approaches, showing that this ambiguity is also
present in sentences in the simple tenses, and that a unified
treatment of for (as well as other temporal adverbials) is
possible once it is recognised that temporal adverbials are
interpreted differently depending on their syntactic position. Rather
than attributing the ambiguity of such sentences to an ambiguity of
the adverbial, I argue that the interpretation of a sentence with a
temporal adverbial is affected by the partition of the sentence into
two portions which are interpreted as parts of different semantic
correlates, much like Topic/Comment, Antecedent/Anaphor and
Background/Focus constructions. Finally, I discuss how a treatment of
``semantic partition'' such as that of Diesing (1992) can be extended
to temporal adverbials and I provide details of how this treatment can
be spelled out in Discourse Representation Theory (Kamp 1981, Heim
1982).
(February 1996; 71 pages)
Ref. No. HCRC/RP-77 Price: UKL 2.40
Anne Cooreman and Anthony J. Sanford
Focus and Syntactic Subordination in Discourse
In two
experiments we test the proposal that the main clauses of complex
sentences influence subsequent attentional focus and that this effect
of syntactic structure competes with other cues. We argue that the
strength of these cues depend on the semantics of the connector and
the type of processing which is required.
The complex sentences in this study contain main and subordinate
clauses linked by the connectors before, after, when, while, because
and since. Our results show a strong dissociation between two
different tasks. A free continuation task showed an overall massive
effect of main clause while a self-paced reading experiment which
measured reading times for target clauses coherent with either main or
subordinate clause of the preceding sentence, showed both main clause
effects and order effects. In both tasks the main clause effect is
strongest with the temporal connectors after and before which require
two temporal reference frames for the mental representation of the
complex clause. The effect of main clause is weakened when readers
are forced to integrate new information as is the case in the reading
task. Here there is no effect of main clause for the connector
because. The results of our study support the findings of Townsend &
Bever (1978) that temporal connectors are processed differently from
causal ones and that overtly expressed causal links direct more
processing to the subordinate clause.
(April 1996; 11 pages)
Ref. No. HCRC/RP-79 Price: UKL 0.70
Steven Bird
Principles of African Tone Orthography Design
Tone languages provide some interesting challenges for the designers
of new orthographies. One approach is to omit tone marks, just as
stress is not marked in English (zero marking). Another approach is to
do phonemic tone analysis and then make heavy use of diacritic symbols
to distinguish the 'tonemes' (exhaustive marking). While orthographies
based on either approach have been successful, this may be thanks to
our ability to manage inadequate orthographies rather than to any
intrinsic advantage which is afforded by one or the other approach. In
many cases, practical experience with both kinds of orthography has
shown that people have not been able to attain the level of reading
and writing fluency that we know to be possible for the orthographies
of non-tonal languages. In some cases this can be attributed to a
sociolinguistic setting which does not favour literacy efforts. In
other cases, the orthography itself might be to blame. If the
orthography of a tone language is difficult to master then a good part
of the reason, I believe, is that the designer either has not paid
enough attention to the function of tone in the language, or
he has not ensured that the information encoded in the orthography is
accessible to the ordinary (non-linguist) user of the
language. If the writing of tone is not going to continue to be a
stumbling block to literacy efforts, then a fresh approach to tone
orthography is required.
This article describes such an approach, as appliued to the tone
languages of sub-Saharan Africa. After describing the problems with
orthographies that use too few or too many tone marks, a wide range of
compromises are surveyed and evaluated. Next, I review the
contributions made by reading theory and linguistic theory. The tone
orthographies of several languages are presented throughout the
article, with particular emphasis on some tone languages of Cameroon.
(December 1996; 42 pages)
Ref. No. HCRC/RP-80 Price: UKL ?.??
Nicholas Asher & Alex Lascarides
Questions in dialogue
In this paper we explore how compositional semantics, discourse
structure and the cognitive states of participants all contribute to
pragmatic constraints on answers to questions in dialogue. We
synthesize formal semantic theories on questions and answers with
techniques for discourse interpretation familiar from computional
linguistics and show how this provides richer constraints on responses
in dialogue than either component can achieve alone.
(May 1996; 38 pages)
Ref. No. HCRC/RP-81 Price: UKL 1.40