Event Representation in Text Understanding
Transfer of Meaning Structures
Haldur Õim
1
and Mare Koit
2
1
Institute of Estonian and General Linguistics, University of Tartu, Jakobi 2, Tartu, Estonia
2
Institute of Computer Science, University of Tartu, Liivi 2, Tartu, Estonia
Keywords: Meaning, Frame, Event, Physical Motion, Communication.
Abstract: When modelling language understanding we have to deal with the process of transferring meanings.
Humans cognize and organize the knowledge about the world, physical as well as social, in such categories
as objects, situations, processes, events, etc., not sentences. The same should hold in a computational model.
In this paper we will consider one kind of these categories, events. We will discuss the possible analogy in
structuring the physical and social events and, accordingly, the possibility to use analogous conceptual and
formal means to represent them.
1 INTRODUCTION
When we want to transfer the text understanding
ability to the computer, we must transfer a theory, a
model of how the understanding system works in
humans because texts we are dealing with are
written by humans. The problem pertains to the
‘units of understanding’. Formally, texts are
concatenations of sentences which are built
according to certain (language-specific) rules. The
upper linguistic level which deals with sentences is
syntax but when modelling language understanding
we must go into semantics and pragmatics which
deal with the process of transferring meanings
(information about the domain dealt with in the text,
and the communicative intentions of the author of
the text). The first point we want to stress is that
here, in describing the understanding process and, in
particular, its results, other units than sentences are
needed. Humans cognize and organize the
knowledge about the world, physical as well as
social, even when they get this knowledge from
texts, in such categories as objects, situations,
processes, events etc., not sentences. The same
should hold in a computational model. We must
have formal representations of such knowledge in
order to use it.
In this paper we will deal with one kind of the
necessary categories, events. Events constitute a
rather specific category in organizing our knowledge
about the world. In a sense, we ‘impose’ these
structures on the continuous flow of what happens
around us. Typically, we remember and talk about
the past in terms of events: they have definite inner
structure, starting and ending states, they can be
organized hierarchically, contain other events as
parts (Tversky et al., 2011). Further, events are
domain-specific. For instance, events of the physical
and social world can be quite different in details.
This means that in understanding and representing
them we have to use not only linguistic, but also
ontological information. On the other hand, events
of different domains can have much in common. In
the cognitive approach to language understanding it
is a commonly accepted thesis that knowledge of
abstract domains is regularly structured using the
structuring of some more concrete domains.
This latter thesis constitutes one of the main
background topics we want to deal with in the
present paper. We have, for quite a long period,
dealt with two domains: (1) motion, agentive as well
as non-agentive (a physical domain) and (2) human
interaction, especially dialogues (a social domain)
(Õim et al., 2010; Koit et al., 2006). Here we will
discuss the possible analogy in structuring the
corresponding events and, accordingly, the
possibility to use analogous conceptual and formal
means to represent the events of both domains. Of
course, it is clear that dialogues as social events have
more complex and specific structure than motion
events. But the general conception underlying both
367
Õim H. and Koit M..
Event Representation in Text Understanding - Transfer of Meaning Structures.
DOI: 10.5220/0004625703670372
In Proceedings of the International Conference on Knowledge Engineering and Ontology Development (KEOD-2013), pages 367-372
ISBN: 978-989-8565-81-5
Copyright
c
2013 SCITEPRESS (Science and Technology Publications, Lda.)
of them has much in common. For instance, both are
dynamic domains. In particular, in dialogues also
‘something’ is moved (from one participant to
another). And since the domain of motion has been
studied in more detail in linguistic as well as in
ontological semantics, it is relevant to ask whether
the results attained here could be used in dealing
with dialogues.
The paper is organized as follows. In Section 2
we consider the structure and representation of
events using frames and qualia structures. Section 3
investigates motion events and Section 4
communication events. Section 5 discusses some
problems and in Section 6 we will make
conclusions.
2 EVENTS AND FRAME
SEMANTICS
The description of the general theoretical framework
of our work can be found, for instance in (Õim et al.,
2010, Õim, 2012). We are using a kind of frame
semantics approach together with qualia structure
approach provided by J. Pustejovsky (1995) and R.
Jackendoff (2002). Events described in sentences are
represented as frames.
The original idea behind the concept of frame
came from frame semantics and specifically from
FrameNet
(see e.g. Fontenelle, 2003 for overview).
Still, for purposes of our study we had to work out
our own inventory of semantic roles. One reason for
this was the need to draw inferences from frames:
FrameNet does not deal with inferences, at least not
explicitly. In case of semantic analysis of text it is
impossible to ignore this problem; and certain kinds
of inferences are directly connected with semantic
roles. This, by the way, does not mean that
FrameNet structures cannot be used to draw
inferences from sentences. We have tried this, in
parallel with our frame structures. But the role
inventory in FrameNet is too complicated and
domain-dependent to be taken as a regular basis of
sentence/text semantic analysis program at the very
beginning.
Frames in our system are structures consisting of
a head – a (motion) verb which in a sentence can
function as predicate – and its possible arguments as
fillers of certain semantic roles. Thus, semantic roles
are the main structuring elements of a frame.
Although the heads of frames are verbs, the frames
are in fact not frames of verbs but frames of events
represented/designated by the verbs as possible
predicates of corresponding sentences. The basic
semantic unit in text semantics is not a word, nor
even a sentence, but an event (in our domain of
motion). The details of one such event can be picked
up from different sentences, they should be collected
and integrated into the frame of this individual
event. A frame is a semantic description of a
predicate, including all of its possible arguments and
their semantic roles. From the point of view of
semantics, the arguments represent participants of an
event and the predicate determines type and the
general structure of the event. Each participant
(argument) has a certain role in the structure.
We are considering complex events described in
texts – the events which include sub-events related
to each other in a certain way, e.g. temporally or
causally. Complex events express dynamics of texts
– which sub-events will cause other sub-events,
which previous sub-events have to be occurred
before a certain sub-event, etc.
Our research data have thus far come mainly
from Estonian but we are compared them with data
from other languages (English, Russian, a. o.).
Related work goes back at least to seventies, e.g.
to the work done by Roger Schank and others on
motion and communication in the frames of
modelling ‘story understanding’ (Schank, 1975,
1986).
His conceptual dependency theory states that
all conceptualizations can be represented in terms of
a small number of primitive acts performed by an
actor on an object (e.g. MTRANS for transferring
mental objects and ATRANS for transferring
physical objects). Events are understood in terms of
scripts, plans and other knowledge structures as well
as relevant previous experiences. (Shank and
Abelson, 1977). Since eighties, the topic of meaning
transfer has intensively been studied in the
conceptual metaphor theory (e. g. Lakoff, 1987).
In the next section we will give an overview of
our conceptualization of motion events. Since we are
interested in using motion as a ‘source domain’ for
structuring (human) communication as the ‘target
domain’, not all details of motion events are of equal
importance. For instance, several physical
characteristics of the entities participating in a
motion event are not relevant in case of
communication events and are omitted here.
3 MOTION EVENTS
The critical difference between an event taken ’as a
whole’ and the ’pure act’ of motion as denoted by
the corresponding predicate or an isolated sentence
KEOD2013-InternationalConferenceonKnowledgeEngineeringandOntologyDevelopment
368
lies in the need to take into account also the
contextual information which should hold and must
be made explicit.
Thus, the meaning of the verb (predicate) ‘to
throw’ as used e.g. in the sentence John threw a
stone from the road into the bushes is usually
described as: an Agent (John) caused an Object
(stone) to move from one place, Locfrom (the road)
to another place, Locto (the bushes). In more
detailed definitions it is added: through the air
(Path). Instrument (the hand of the Agent) and Path
(the air) represent so-called hidden arguments (see
Jackendoff, 2002, Õim, 2012). But even adding
them to the throwing-event frame does not make the
whole event as expressed in the above sentence
ontologically explicit because in fact we have here a
complex event, i.e. an event containing sub-events
some of which may, in the general-semantic sense,
not constitute an obligatory part of throwing. For
instance, before the throwing act proper John must
have picked up the stone from the road, etc.
FRAME: AGENTIVE_MOTION
HYPERONYM: MOTION
PRECONDITIONS: Agent has Object
ACT:
ROLE STRUCTURE
Participant Roles
ROLE: Agent (the instigator of the
event)
ROLE: Object (the entity which
moves)
FRAME: Location_1
Object = Object
Loc = Locfrom
Time = Timefrom
FRAME: Location_2
Object = Object
Loc = Locto
Time = Timeto
ROLE: Instrument (e.g. with hands)
ROLE: Locfrom (place where the
motion starts)
ROLE: Loc (place where the motion
occurs)
ROLE: Locto (place where the motion
ends)
ROLE: Direction
ROLE: Path (e.g. over a bush)
ROLE: Manner (e.g. slowly, angrily)
ROLE: Quant (e.g. how many times)
ROLE: Goal (of the Agent: Object is
located at Locto).
CONSEQUENCES: Agent does not have
Object
Figure 1: The frame AGENTIVE MOTION.
In Fig.1, the frame structure of AGENTIVE
MOTION is given in basic details (where Agent
intentionally moves Object from one place to
another, as represented by verbs like ‘to throw’ or
‘to lift’). Each role puts requirements to its fillers,
e.g. Object of agentive motion has to be a physical
object. There are different requirements in the case
of the roles of the frames of different verbs.
The Location sub-frames are attached to the roles
whose fillers move in the event described by the
frame. In the described type of the motion event
Object represents the only entity that obligatorily
moves. Location_1 and Location_2 fix the location
of the entity before and after the motion event,
accordingly, taking the corresponding information
from the Locfrom and Locto roles of the main
frame.
In our general model, we make a distinction
between motion participants and motion space, that
is entities that move and that represent the
’environment’ of motion. Typical motion
participants are the fillers of the roles Agent, Object
and Instrument, and motion space is determined by
the fillers of Loc, Locfrom, Locto, Path. This is an
ontological distinction specific to physical motion
and, as said above, we will not consider it more
closely here (but see Õim, 2012). We will return to
the problem in Section 5.
In our research we are proceeding in the
following way. We have chosen a number of
predicates (verbs) that represent certain types of
motion events (moving on the ground, in the air or in
the water, using certain instruments, e.g. body-parts
or vehicles, etc.). Departing from these predicates,
we have collected examples from corpora and
(multilingual) dictionaries, seeking for ontologically
representative types of entities that can function as
the fillers of the semantic roles in the corresponding
motion events. The aim is to build a typology of
entities that function as motion participants and
motion spaces, and on this basis, the typology of
motion events.
4 COMMUNICATION EVENTS
When communicating, the speakers can perform
actions while making utterances. Such actions are
called speech acts (asserting, commanding,
requesting, etc.). The participants express certain
attitudes, and the type of speech act being performed
corresponds to the type of attitude being expressed.
For example, a statement expresses a belief, and a
request expresses a desire.
EventRepresentationinTextUnderstanding-TransferofMeaningStructures
369
A speech act, or a communicative act, is a minimal
functional unit in human communication. Every act
predicts in certain degree, which another act can
follow (e.g. a question has to be answered by a
communication partner, a request granted, etc.).
Every act can be considered as a (motion) event in
communication and the dialogue itself is a complex
event which includes communicative acts related to
each other.
We consider communication between two
participants, A and B, where the goal of A is to get
some information. Our empirical material is a
dialogue corpus which contains different types of
dialogues, among them authentic telephone
conversations (see the following excerpt of a
transcribed directory inquiry taken from the corpus).
A: öelge palun linnaliini bussijaama
infotelefoni number. REQUEST
please tell me the phone number of the
town bus station
B: kolm kuus kaks GIVING INFORMATION
three six two
A: jah CONTINUER
yes
B: seitse kuus seitse.
GIVING INFORMATION
seven six seven
Communicative acts as motion events (used to
forward and receive information) can be represented
as frames where the moving object is information.
The frame of the communicative act REQUEST is
shown in Fig.2.
The author of the act, A (Agent) is forwarding
his/her request to the addressee, B (Recipient),
information (A’s request) is moving from A to B.
The author and the addressee themselves do not
move, they can be even on different places and
communicate by telephone.
Unlike of agentive motion (Fig.1), every
communicative act obligatorily has two ‘intentional’
participants, although in different roles (Agent and
Recipient). The moving object is non-physical
(information), and Agent does not lose information
forwarded to Recipient (which is different when
moving physical objects).
Communication as a complex event can be
considered as a temporal sequence of sub-events –
communicative acts – and can be represented as a
motion frame which contains other motion frames
inside itself. In the simplest case, a dialogue consists
of two communicative acts, e.g. question – answer:
A asks a question and B answers it (Fig. 3).
FRAME: REQUEST_for_information
HYPERONYM: COMMUNICATIVE_ACT
PRECONDITIONS
A believes that there exists d
D such that p(d/x) is true
A wants to know the element of
D which satisfies p
A believes that B knows the
element of D which satisfies p
GOAL: B knows that A wants to know the
element of D which satisfies p
ACT: A informs B that A wants to know
which element of D satisfies p
ROLE STRUCTURE
Participant Roles
ROLE: Agent (A)
FRAME: Location_1
Object: Agent
Loc: Locfrom
ROLE: Recipient (B)
FRAME: Location_2
Object: Recipient
Loc: LocTo
ROLE: Object (information which moves
from A to B)
FRAME: Location_1
Object = Object
Loc = Locfrom
Time = Timefrom
FRAME: Location_2
Object = Object
Loc = Locto
Time = Timeto
ROLE: Instrument (voice)
CONSEQUENCE: B knows that A wants to
know the element of D which satisfies p
Figure 2: Communicative act REQUEST for information.
Information is moving from one participant to
another: from A to B (question) and from B to A
(answer). In the same time, both A and B keep
information which has been forwarded to the
partner, therefore, their knowledge is increasing in
the communication process. The fillers of the roles
of Agent and Recipient are changing during
communication (while A and B are turn-taking).
Still, miscommunications can occur when
exchanging information, e.g. Recipient does not hear
or does not understand information (request)
forwarded by Agent, or s/he does not have
information requested by Agent (i.e. some of
preconditions does not hold).
KEOD2013-InternationalConferenceonKnowledgeEngineeringandOntologyDevelopment
370
FRAME: EXCHANGE information
HYPERONYM: COMMUNICATION
PRECONDITIONS:
A has INFO_A
B has INFO_B
ACT:
FRAME: COMMUNICATIVE_ACT_A
AGENT: A
RECIPIENT: B
OBJECT: INFO_A
INSTRUMENT: voice A
TIME: T1
GOAL: B has INFO_A
FRAME: COMMUNICATIVE_ACT_B
AGENT: B
RECIPIENT: A
OBJECT: INFO_B
INSTRUMENT: voice B
TIME: T2 (> T1)
GOAL: A has INFO_B
CONSEQUENCE:
B has INFO_A
A has INFO_B
Figure 3: Exchange of information as a complex event.
5 DISCUSSION
In text understanding, it is necessary to draw
inferences in order to add information not presented
in text explicitly. Linguistic-semantic inferences
determined by semantics of a predicate can be
included into the corresponding frame, e.g. as it was
done in the frame of throwing in the Object role and
in two frames of communicative events in the
previous section. In addition, our frame structure
suggests the use of a general inference scheme:
IF Act is true at time t THEN
Preconditions are true at t
1
< t and
Consequences are true at t
2
> t.
In other words, if Recipient knows that Act is
performed then s/he knows also which preconditions
were true before performing Act and which
consequences hold after performing Act.
Another and more complicated problem is
representing ontological or, in general, situation-
driven inferences. For instance, events proceed not
always as planned by the Agent. Thus, in the
sentence John put the ball on the table but it rolled
down to the floor the ultimate location of the ball is
not the table as it would be fixed in the frame of to
put (in the roles Locto and Goal). Formally, this is a
complex event where two motion events involving
the same Object follow immediately each other and
thus the ultimate location of the ball is easy to fix.
When ‘processing’ the given sentence we
understand also the connection between the events –
why the rolling event occurred at all (at least
supposedly). It is an example of the situation where
the interaction between motion participants and
motion space discussed in short in Section 3 comes
into play: the rolling object must have certain shape
and the ground must be relatively flat; and in the
given case the top of the table was not quite
horizontal, etc.
It is an example of the situation where the
interaction between motion participants and motion
space discussed in short in Section 3 comes into
play: the rolling object as motion participant must
have certain shape and the ground as motion space
must be relatively flat; and in the given case the
ground (top of the table) was not quite horizontal,
etc.
The important fact to point out here is that the
same kinds of unplanned events can occur (and can
be dealt with) in communication as well. For
instance, when A tells something to B with the goal
that B will know the information, accept it, respond
to it etc., it can happen that B does not hear A, does
not understand what s/he said, or decides to not
accept it or not respond to it. Analogous why-
questions appear in understanding such events.
Thus, a similar typology of forwarded information
units and of the parameters of communication space
and their interactions has to be worked out. We have
already made some investigations in (Koit and Õim,
2004; Hennoste et al., 2005).
6 CONCLUSIONS AND FUTURE
WORK
Texts used in human communication rely heavily on
the background knowledge that the participants are
supposed to have and, because of this, are not
explicitly stated in text. When we are dealing with
the semantic analysis of texts by the computer, this
knowledge must be made explicit: it is critically
relevant for constructing a coherent picture of the
events, processes etc. described in a text, so that the
computer would be able to fill in the ‘data gaps’, by
taking the lacking data from its domain model, by
making inferences about the event itself, about the
participants, and so on.
In general, most of the motion events we are
used to treat as compact and simple ones in fact
EventRepresentationinTextUnderstanding-TransferofMeaningStructures
371
appear to be complex, especially in the context of a
concrete text, and should be represented as
‘compositions’ of sub-events. Formally, the sub-
events have the same structure as motion frames in
general, but the critical requirement is that the
prerequisites and consequences of sub-events, as
well as the fillers of the corresponding semantic
roles should fit each other in different sub-events in
the way determined by the cover event.
Dialogues as social events have more complex
and specific structure than physical motion events.
But the general conception underlying both of them
has much in common: both domains are dynamic,
something is moving also in dialogues. The domain
of physical motion has been studied in more detail in
semantics therefore the results attained here could be
used also in dealing with dialogues.
Our further work will be focused on typology of
the features of the entities and their interrelations in
physical motion as well as in social domain. The
central aim, in studying the domain of motion, is to
build a typology of entities that function as motion
participants and motion spaces, and on this basis, the
typology of motion events. The same type of
research will be done in the domain of
communication. Departing from these results, some
conclusions and generalizations should be possible
to make about how the process of understanding
texts (and the world) is organized in humans and
how these processes could be more adequately
modelled on the computers.
ACKNOWLEDGEMENTS
This work is supported by the European Regional
Development Fund through the Estonian Centre of
Excellence in Computer Science (EXCS), the
Estonian Research Council (grant ETF9124), and the
Estonian Ministry of Education and Research (grant
SF0180078s08). The authors thank the anonymous
reviewers.
REFERENCES
Fontenelle, T. (ed.), 2003. International Journal of
Lexicography. Special issue, 16 (3).
Hennoste, T., Gerassimenko, O., Kasterpalu, R., Koit, M.,
Rääbis, A., Strandson, K., Truu, T., Valdisoo, M.,
2005. Miscommunication in Spoken Dialogues and Its
Modelling in a Dialogue System. In Proc. of SPECOM
2005. 10th International Conference on Speech and
Computer, 413–416. Patras, Greece.
Jackendoff, R., 2002. Foundations of Language. Brain,
Meaning, Grammar, Evolution, Oxford University
Press. New York.
Koit, M., Õim, H., 2004. Argumentation in the Agreement
Negotiation Process: A Model that Involves Natural
Reasoning. In Proc. of the Workshop W12 on
Computational Models of Natural Argument. 16th
European Conference on Artificial Intelligence, 53–
56. Valencia, Spain,
Koit, M., Valdisoo, M., Gerassimenko, O., Hennoste, T.,
Kasterpalu, R., Rääbis, A., Strandson, K., 2006.
Processing of Requests in Estonian Institutional
Dialogues: Corpus Analysis. In Text, Speech and
Dialogue, Proceedings, 621–628.
Lakoff, G., 1987. Women, Fire, and Dangerous Things,
University of Chicago Press. Chicago.
Õim, H., 2012. Ontological Features of Entities in Motion
Events and Their Role in the Semantic Analysis of
Sentences. In Human Language Technologies – The
Baltic Perspective, 280–285, IOS Press. Amsterdam etc.
Õim, H., Orav, H., Kahusk, N., Taremaa, P., 2010.
Semantic analysis of sentences: the Estonian
experience. In Human Language Technologies – The
Baltic Perspective, 208–216, IOS Press. Amsterdam etc.
Pustejovsky, J., 1995. The Generative Lexicon, The MIT
Press. Cambridge, Mass.
Schank, R. C., 1986. Explanation Patterns:
Understanding Mechanically and Creatively,
Hillsdale, NJ Lawrence Earlbaum Associates.
Schank, R. C., 1975. Conceptual Information Processing,
Elsevier. New York.
Schank, R. C., Abelson, R. B., 1977. Scripts, Plans, Goals
and Understanding: An Inquiry into Human
Knowledge Structures. Hillsdale, NJ Lawrence
Earlbaum Associates.
Tversky, B., Zacks, J. M., Morrison, B. J., Hard, M. B.,
2011. Talking about events. In J. Bohnemeyer, E.
Pedersen (eds.) Event representation in language and
cognition, 216–227. CUP. Cambridge etc.
KEOD2013-InternationalConferenceonKnowledgeEngineeringandOntologyDevelopment
372
