leff@smu.CSNET (Laurence Leff) (05/23/87)
Below are the abstracts of forthcoming publications from USC/Information
Sciences Institute. If you wish to receive copies of any of these reports,
please contact:
Diane Speekman
USC/Information Sciences Institute
4676 Admiralty Way, Ste. 1001
Marina del Rey, CA 90292-6695
Copies of all USC/ISI reports may be obtained by writing (about three months
after publication) to National Technical Information Service, Springfield, VA
22151.
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ANTITHESIS: A STUDY IN CLAUSE COMBINING AND DISCOURSE STRUCTURE
William C. Mann
Sandra A. Thompson
ISI/RS-87-171
April 1987
approx. 30 pages
AI research in text generation needs a strong linguistically justified
descriptive theory as a basis for creating methods by which programs can write
multiparagraph texts. This paper sketches Rhetorical Structure Theory, which
has been designed to support text generation, and then applies RST to
describing a particular class of discourse constructs.
There is no consensus as to the status of clause combining relations relative
to larger texts. This paper demonstrates a clause combining relation that is
also found as part of larger text structures, and shows how this fact can be
used to explain cases in which contrastive clause combining appears between
clauses that are not in fact in contrast. The appropriate generalization is
that the relations of clause combining and the relations of general text
structure are the same. Use of this generalization should make AI text
planning and text generation significantly easier.
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NOTES ON THE ORGANIZATION OF THE ENVIRONMENT OF A TEXT GENERATION GRAMMAR
Christian Matthiessen
ISI/RS-87-177
April 1987
approx. 52 pages
One of the tasks in designing a text generation system is to organize the
environment of the grammatical component of the generation system in such a
way that it supports the grammatical resources in generation. This report
discusses the methods used for the Penman generation system to infer aspects
of the organization of the knowledge base and other components of the
environments of the Nigel grammar of the Penman system. It is shown how the
design task can be broken down into a number of very explicit demands on the
environment. In the main part of the report, the results of application of
such an approach is sketched, with particular emphasis on the general
organization of the knowledge base and the discourse model parts of the
environment.
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SYSTEMIC GRAMMAR AND FUNCTIONAL UNIFICATION GRAMMAR
- and -
REPRESENTATIONAL ISSUES IN SYSTEMIC FUNCTIONAL GRAMMAR
Christian Matthiessen
Robert Kasper
ISI/RS-87-179
April 1987
approx. 55 pages
SYSTEMIC GRAMMAR AND FUNCTIONAL UNIFICATION GRAMMAR: Systemic Functional
Grammar (SFG) and Functional Unification Grammar (FUG) are superficially very
different approaches to grammatical knowledge, but they share an underlying
comparability that runs very deep. FUG shares with systemic descriptions an
emphasis on the functions of linguistic objects, and an explicit
representation of feature choices. This paper explores how a systemic
grammar can be represented in FUG notation, as a step toward creating a
grammatical analysis program for English. Because FUG has been developed as a
computational tool, expressing a systemic grammar in FUG notation allows new
computational techniques to be applied to it. Among other benefits, this
program will make it possible to study how much the grammatical functions of
sentences are recoverable from them. It will also provide a method to test the
amount of ambiquity implicit in a systemic description, a topic which has so
far been inaccessible. This use of FUG as an alternate representation for SFG
may have some additional benefits for both frameworks. It provides some
solutions to problems in systemic notation which are described by Matthiessen
(in this volume). Several extensions to the FUG framework are also suggested
by this study.
REPRESENTATIONAL ISSUES IN SYSTEMIC FUNCTIONAL GRAMMAR: Nigel is a large
diverse computational grammar for text generation. Its
framework is an implementation of Systemic Functional Theory of grammar and it
constitutes a context in which the representation of systemic theory can be
explored and studied.
This paper surveys the representational devices used in the Nigel grammar and
the representational issues that they raise in relation to systemic theory.
These issues are diagnosed in the light of the metafunctional differentiation
of systemic theory.
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ROUTING AND ADDRESSING PROBLEMS IN LARGE METROPOLITAN-SCALE INTERNETWORKS
Gregory G. Finn
ISI/RR-87-180
March 1987
approx. 61 pages
Digital packet networking technology is spreading rapidly into the commercial
sector. Currently, most networks are isolated local area networks. This
isolation is counterproductive. Within the next twenty years it should be
possible to connect these networks to one another via a vast internetwork. A
metropolitan internetwork must be capable of connecting many thousand networks
and a national one several million. It is difficult to extend current
internetworking technolgy to this scale. Problems include routing and host
mobility. This report addresses these problems by developing an algorithm
that retains robustness and has desirable commercial characteristics.
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TEXT GENERATION: THE PROBLEM OF TEXT STRUCTURE
William C. Mann
ISI/RS-87-181
March 1987
approx. 22 pages
One of the key problems in AI text generation is text organization. A poorly
organized text can be unreadable or even misleading. Two AI approaches to
text organization are compared: McKeown's TEXT system and Rhetorical Structure
Theory (RST).
They share many assumptions about the nature of text yet they are found to be
in strong contrast. TEXT identifies text organization with whole-text
nonrecursive structures, while RST uses small recursive ones. RST has an
elaborate apparatus of relations between parts of texts, and of the
"nuclearity" of particular parts; TEXT has no correlates for these. RST works
with a wide range of relation types, TEXT with just one of them. TEXT has no
correlates for these. RST works with a wide range of relation types, TEXT
with just one of them. TEXT is an implemented system, whereas RST is
developmental. Most important, TEXT develops text organizations so that they
resemble patterns extracted from previous text, while RST strives for an
organization which is justifiable as meeting the goals of the text being
generated.
This contrast raises many of the key issues discussed in this paper about the
nature of text organization and how it can be created by programs.
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A REVIEW OF CONCEPTUAL STRUCTURES:
INFORMATION PROCESSING IN MIND AND MACHINE
Stephen Smoliar
ISI/RS-87-182
March 1987
approx. 8 pages
This is a review of the book Conceptual Structures: Information Processing in
Mind and Machine, by John F. Sowa, published in 1984 by the Addison-Wesley
Publishing Company.
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THE STRUCTURE OF DISCOURSE AND "SUBORDINATION"
Christian Matthiessen
Sandra A. Thompson
ISI/RS-87-183
April 1987
The use and nature of clause combining in natural discourse are explored in
this paper. First, a theory of text structure, Rhetorical Structure Theory,
is introduced and illustrated for a number of short texts. Then, it is shown
how the grammar of clause combining can be explained in terms of the
structuring of text. The paper focuses on one particular way of combining
clauses and shows how it is used to express a nuclear-satellite structuring of
text identified by Rhetorical Structure Theory.
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RELIABILITY AND PERFORMANCE MODELLING OF HYPERCUBE-BASED MULTIPROCESSORS
Walid Najjar
Jean-Luc Gaudiot
ISI/RS-87-184
April 1987
New technologies of integration now enable the design of computing systems
with dozens and even hundreds of independent homogeneous Processing Elements
which can cooperate on the solution of the same problem for a corresponding
improvement in the execution time. However, as the number of Processing Units
increases, concerns for reliability and continued operation of the system in
the face of failures must be addressed. A commonly used network topology, the
hypercube, is analyzed in this paper. It is shown how the disconnection of a
subset of the machine would yield a total system failure. Overall reliability
measures as well as computational availability, etc., are derived by a
combination of analytical modelling and simulation approaches (Monte Carlo
simulation). Finally, a comparison with other topologies (mesh connected
network, etc.) shows the influence of the connectivity of the network on the
reliability of the system.
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RHETORICAL STRUCTURE THEORY:
A FRAMEWORK FOR THE ANALYSIS OF TEXTS
William C. Mann
Sandra A. Thompson
ISI/RS-87-185
April 1987
Rhetorical Structure Theory is a theory of text organization which provides a
framework for an analysis of text. The theory is based on the understanding
that a text is not merely a string of clauses, but consists instead of
hierarchically organized groups of clauses that stand in various relations to
one another. These "rhetorical relations" can be described functionally in
terms of the purposes of the writer and the writer's assumptions about the
reader. They hold between two adjacent parts of a text, where, typically, one
part is "nuclear" and one a "satellite." An analysis of a text consists in
identifying the relations holding between successively larger parts of the
text, yielding a natural hierarchical descriptions of the rhetorical
organization of the text.
The paper informally outlines RST's mechanisms and applications, which include
studies of clause combining, coherence and assertional effects of discourse
structure. RST characteristically provides comprehensive analyses rather than
selective commentary. RST is insensitive to text size, and has been applied
to a wide variety of sizes of text.
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INTERPRETATION IN GENERATION
Eduard H. Hovy
ISI/RS-87-186
April 1987
The computer maxim "garbage in, garbage out" is especially true of language
generation. When a generator slavishly follows its input topics, it usually
produces bad text. In order to find more appropriate forms of expression,
generators must be given the ability to interpret their input topics. Often,
newly-formed interpretations can help generators achieve their pragmatic goals
with respect to the hearer. Since interpretation requires inference,
generators must exercise some control over the inference process. Some
general strategies of control and some specific techniques, geared toward
achieving pragmatic goals, are described here.
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A UNIFICATION METHOD FOR DISJUNCTIVE FEATURE DESCRIPTIONS
Robert Kasper
ISI/RS-87-187
April 1987
Although disjunction has been used in several unification-based grammar
formalisms, existing methods of unification have been unsatisfactory for
descriptions containing large quantities of disjunction, because they require
exponential time. This paper describes a method of unification by successive
approximation, resulting in better average performance.
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SEMANTICS FOR A SYSTEMIC GRAMMAR:
THE CHOOSER AND INQUIRY FRAMEWORK
Christian Matthiessen
ISI/RS-87-189
May 1987
This report describes the semantic interface between a systemic functional
grammar for text generation and the environment the grammar operates in. The
grammar is organized as a network of choice points and the semantic interface
provides a method for making the grammatical choices in a purposeful way.
Each grammatical choice point is equipped with its own semantic procedure for
choosing: one or more questions are addressed to one of the components of the
environment, such as the knowledge base, so that the information needed to
select the appropriate choice alternative can be obtained. The paper presents
the framework as a kind of semantics for systemic grammars and also relates it
to other semantic approaches.