Towards Pragmatic Production Strategies for Natural Language Generation Tasks Mario Giulianelli

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Towards Pragmatic Production Strategies
for Natural Language Generation Tasks
Mario Giulianelli
Institute for Logic, Language and Computation
University of Amsterdam
m.giulianelli@uva.nl
Abstract
This position paper proposes a conceptual
framework for the design of Natural Lan-
guage Generation (NLG) systems that follow
efficient and effective production strategies
in order to achieve complex communicative
goals. In this general framework, efficiency is
characterised as the parsimonious regulation
of production and comprehension costs while
effectiveness is measured with respect to
task-oriented and contextually grounded
communicative goals. We provide concrete
suggestions for the estimation of goals, costs,
and utility via modern statistical methods,
demonstrating applications of our framework
to the classic pragmatic task of visually
grounded referential games and to abstractive
text summarisation, two popular generation
tasks with real-world applications. In sum, we
advocate for the development of NLG systems
that learn to make pragmatic production
decisions from experience, by reasoning about
goals, costs, and utility in a human-like way.
1 Introduction
Novelists choose the right words to keep readers
engaged and enthused, good journalists can con-
vey facts clearly and convincingly, while poets
may want to surprise the reader. Teachers adapt
their explanations to the level of their students,
and the language of parents changes with the pro-
ficiency of their children, with the same objects
described first using simplified funny expressions
(‘moo moo’) and then more informative and dis-
criminative names (‘cow’,‘calf). Using language
to communicate successfully requires effort. On
the side of the language producer, it is first of all ef-
fortful to come up with words that truthfully corre-
spond to one’s communicative intent. Then, words
must be actually produced, e.g. said out loud or
typed on a keyboard. At the same time, the pro-
ducer has to take into consideration whether the
comprehender—for whom, too, linguistic commu-
nication is costly—will be able to infer the original
intent. Comprehenders make efforts to pay atten-
tion to the utterance they are being addressed with,
to interpret it, and to infer their interlocutor’s com-
municative intent. Fortunately, these efforts are
often not in vain. They allow people to exchange
knowledge, ideas, plans, and to achieve goals.
This paper introduces a conceptual framework
for Natural Language Generation (NLG) in vari-
ably complex communicative scenarios, which re-
lies on three main notions:
communicative goals
,
production and comprehension
costs
, and
utility
.
We define these notions formally and then, in two
case studies, we provide suggestions for their op-
erationalisation in classic NLG tasks. In sum, we
model humans as decision makers striving for effi-
cient and effective communication, and argue that
human-like linguistic behaviour emerges as a result
of reasoning about goals, costs, and utility. Learn-
ing to navigate the complex decision space defined
by these notions is still an open problem: we dis-
cuss possible promising directions.
2 Doing Things with Words
Communication always comes with a goal: speak-
ers use words to change the state of the world. In
this section, we give a characterisation of commu-
nicative goals, discuss the types of effort (or costs)
necessary to achieve goals, and describe the re-
wards associated with successful communication.
2.1 Communicative Goal
What do speakers do with words? The communica-
tive goal (or communicative intent) of a speaker
can be formulated as a function of the current state
of the world wW:
Gs:WW, w 7→ w(1)
where
w
is the intended future state of the world.
Speaker
s
and audience
a
are included in
w
as
they can be both conceptualised, and there is ev-
idence that they are processed (Brown-Schmidt
arXiv:2210.12828v1 [cs.CL] 23 Oct 2022
et al.,2015), as parts of the state of the world. For
communication to be successful, the audience must
be able to reconstruct the original communicative
goal: their decoded transformation of the world,
Da:WW
, must be such that
Da(w)Gs(w)
.
1
Communicative goals shape and constrain a
speaker’s production choices: different utterance
types typically correspond to different goals. The
communicative goal of a referring utterance (“The
black and white cat”), for example, is a state of
the world where the audience is able to identify an
entity in context. The transformation
Da
required
to achieve
w
is a change of attention by the
audience. Statements (“The Sun is a star”) are
typically used when the purpose of an interaction is
pure information transmission—e.g., when giving
a scientific talk. In this case, the communicative
goal is a state of the world in which the audience
holds new beliefs, the ones intended by the speaker.
Da
is a transformation of the belief state of the
audience, and the communicative goal is achieved
when
Da(w)Gs(w)= w
. All utterance types—
e.g., questions, directives, and performatives—can
be seen as strategies to achieve communicative
goals. The same utterance type, and even the same
utterance, can fulfil different goals: a blatantly
false statement (“It never rains in Amsterdam”)
can be used for comedic effect rather than for
conveying facts. For simplicity, in the rest of this
paper, we describe utterances as having a single
communicative goal. Often, however, different
goals are associated with the same utterance at
the same time: a teacher can use a question (“Are
you sure this is the right answer?”) to inform
their student that their answer is incorrect, while
showing a positive attitude towards them—thereby
striving for both epistemic and social utility. Our
framework naturally generalises over such cases;
when multiple communicative goals are involved,
states of the world can be designed accordingly.2
2.2 Production Costs
Given the current and the intended future state
of the world,
w
and
w=Gs(w)
, a speaker en-
codes the communicative goal
Gs(w)
into a mental
representation of the intended state of the world:
1
We sometimes refer to
Da(w)
and
Gs(w)
as
Da
and
Gs
,
as in our formulation these functions are always applied to the
current state of the world w.
2
To account for epistemic and social utility, for example,
states of the world can be defined to include the audience
belief state as well as their emotional state.
Es(Gs(w))= e
. To use a slightly different vocabu-
lary, this is the speaker’s conception of the intended
environment state. The speaker then realises
e
as
an utterance
r
which is presented to the audience:
Rs(e) = r
. Two types of cost are associated with
the encoding and realisation processes. Because
the encoding process is inevitably lossy—mental
representations are compressed representations of
the real state of the world—the speaker makes an
effort to reduce information loss; we refer to this
as the
encoding cost CE
. The cost associated with
executing a bit of behaviour
r
meant to be per-
ceived by the audience (e.g., speaking, writing, or
typing) is the
realisation cost CR
. Both costs af-
fect the decision making process of speakers. In
addition, the speaker is influenced by the expected
comprehension costs of the audience.
2.3 Comprehension Costs
The speaker’s communicative goal
Gs(w)
is not
observable by comprehenders. Given a state of the
world
w
and the speaker’s behaviour
r
, compre-
henders process
r
into a reconstruction of the orig-
inal mental representation,
Pa(r) = e0e
, from
which they decode the speaker’s communicative
goal:
Da(e0)= w0Gs(w)
. Two types of cost are
associated with the comprehension of an utterance.
Speaker and comprehender are different individu-
als and therefore have different ways of encoding
communicative goals into messages (Connell and
Lynott,2014). In the absence of a perfect model of
the speaker’s encoding mechanism, reconstructing
e
is a lossy and effortful process; we denote the
corresponding cost as
processing cost
,
CP
. The
second cost results from interpreting
e0
in context—
i.e., decoding from
e
the state of the world intended
by the speaker. In other words, this is the effort
required to ground the message in the environment.
We refer to it as the
decoding cost CD
. It is impor-
tant to note that although processing and decoding
costs are on the side of comprehenders, speakers
estimate them and take them into account when
making production decisions.
2.4 Utility
In what ways is the decision making process
of speakers affected by these costs? Speakers
are thought to be driven by efficiency concerns
(Zipf,1949;Jaeger and Tily,2011): they strive
to minimise the collaborative effort required
to achieve their communicative goals (Clark
and Wilkes-Gibbs,1986;Clark and Schaefer,
摘要:

TowardsPragmaticProductionStrategiesforNaturalLanguageGenerationTasksMarioGiulianelliInstituteforLogic,LanguageandComputationUniversityofAmsterdamm.giulianelli@uva.nlAbstractThispositionpaperproposesaconceptualframeworkforthedesignofNaturalLan-guageGeneration(NLG)systemsthatfollowefcientandeffectiv...

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