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Paper
The obligations and common ground structure of practical dialogues Luis A. Pinedaa, Varinia M. Estradaa, Sergio R. Coriaa, James F. Allenb
a Instituto de Investigaciones en Matemáticas Aplicadas y en Sistemas (IIMAS)
Universidad Nacional Autónoma de México (UNAM)
b Department of Computer Science, University of Rochester
In this paper a theory of dialogue structure of task oriented conversations and its associated tagging scheme are presented. The theory introduces two linguistic structures supporting the dialogue that, following traditional terminology, we call the obligations and common ground. The theory is illustrated with the detailed analysis of a transaction. We also describe the empirical work supporting the theory, as well as an evaluation task. The paper is concluded with a reflection on the relation of the present theory to traditional notions of obligations and grounding, its relation to a more general theory of discourse and conversation and its potential application to the construction of spoken natural language systems. Keywords: Conversational structure, obligations and common ground, dialogue models, dialogue managers. 1. Introduction
pant. For instance, an action directive stated by U
(user) creates the obligation on S (system) to
In this paper it is postulated that transactions in task
perform the specified act, provided that social and
oriented conversations or practical dialogues [2] are
other contextual conditions hold. The structure of
supported by two linguistic structures that we call
obligations is defined as the relation between the
the obligations and the common ground. These
speech acts that state this kind of intentions and the
structures are ‘built’ by the speech or dialogue acts
speech acts that satisfy them, within conversational
performed by the conversational participants, and a
transactions. This structure is based on such a strong
task oriented transaction is successfully concluded
traditions and social conventions that is even
when the construction of these two structures comes
satisfied in non-cooperative conversations (e.g. [9]).
The common ground structure, on the other hand, is
The structure of obligations involves the specifi-
defined as the relation between the speech acts
cation of intentions through the realization of speech
through which conversational participants make
acts by one conversational participant, and the
sure that they share a common set of beliefs and
satisfaction of such intentions through linguistic
intentions, and understand the utterances performed
acts, or perhaps through acts expressed in alter-
by their partners as intended [5]. In an idealized
native modalities, by the same or the other partici-
conversation, every speech act is understood as
Inteligencia Artificial, Revista Iberoamericana de Inteligencia Artificial. Vol 11, No. 36 (2007), pp. 9-17. ISSN: 1137-3601. AEPIA (http://www.aepia.org/revista).
Inteligencia Artificial V. 11, Nº 36, 2007
intended as soon as it is performed, and an implicit
discussion of the theory, including its relation to
common ground is held between participants along
previous work on obligations and grounding, and its
the whole of the conversation; however, in real
potential applications for developing conversational
commonly interrupted and needs to be reestablished
in order to proceed with the conversation. The
common ground can be broken in two main types of
2. The DIME-DAMSL Tagging Scheme
situations: due to a lack of agreement between the
The notions of conversational obligations and
understanding problem. In the former case a speech
grounding have large tradition in philosophy, lin-
act is listened well but the hearer fails to agree with
guistics, psychology and AI, and have been applied
part or all of its content. The latter case is
to the definition of dialogue managers [1,9];
exemplified by situations in which the message is
however, these structures are not reflected directly
not clear due to noise, for instance, and explicit
in annotation schemes, like DAMSL [6,3], which
speech acts are required to ensure that the
has been used for dialogue analysis [1]. DAMSL
participants are ‘engaged’ in the conversation. We
distinguishes between the communicative status, the
also postulate that the understanding plane includes
information level and the forward and backward
situations in which the referent is not determined
looking functions of utterances, but discourse obli-
enough due to its ambiguous or vague nature.
gations and common ground acts are distributed
implicitly in these four main dimensions. In par-
Speech acts need to be distinguished from the
ticular, utterances expressing obligations, like ac-
utterances that express them, and the same utter-
tion directives or information requests, are the
ance may express more than one speech act, possi-
prominent part of the forward looking functions, but
bly in different conversational structures. For in-
there are also forward looking functions related to
stance, an okay may express a commit in the obli-
the common ground, like an affirm act introducing
gations structure, an accept in the agreement plane,
new information, that must be acknowledged by the
and an acknowledgment in the understanding plane
hearer; conversely, although most explicit tags of
the backward looking functions are mainly
concerned with grounding, there are also some
There are constraints on the relation between speech
backward functions, like answers, that belong to the
acts; an action directive, for instance, needs to be
paired with an action, and an information request
with an answer; in the common ground, a hold act
In the present investigation we develop on the
must be paired with an accept act, when the
DAMSL tagging scheme and, on the basis of the
assertion that was put on hold is finally agreed upon,
analysis of the DIME Corpus1, the DIME-DAMSL
and an overt misunderstanding signal, like what did
tagging scheme has been introduced [8,10]. In this
you say?, must be paired with an utterance that
scheme, all four dimensions of DAMSL are
supplies the missing information. If a transaction
considered, but in addition, the structure of
satisfies all the stated constrains it is said that it is
obligations and common ground is made explicit;
the specification of this structure includes the
definition of a set of speech act types, and also the
Summarizing, we define the obligations and
specification of the constraints that the actual
common ground structure as the relation between
performance of these acts should satisfy. This
speech acts in a conversational transaction, in addi-
relation is defined in terms of the ‘charge’ and
tion to a number of constraints on such relation. In
‘credit’ import of these acts; for instance, an action
the rest of this paper, the specification of a theory of
directive creates an obligation’s charge, and this
dialogue acts and conversation based on the ex-
charge is only credited when the corresponding
plicit realization of the obligations and common
action is performed later on in the transaction.
ground structure is presented. In Section 2 the basic
theory and its associated tagging scheme are
An action directive charges the common ground too,
introduced. In Section 3, the theory is illustrated
but this charge is credited immediately as soon as
with the analysis of a transaction of a task oriented
the act is understood and agreed upon by the
conversation. In Section 4 a summary of the em-
interlocutor. In accordance with basic accountability
pirical work supporting the theory and an evalua-
tion exercise are presented. Finally, in Section 5, a
1 http://leibniz.iimas.unam.mx/~luis/DIME/ Inteligencia Artificial V. 11, Nº 36, 2007
principles, a transaction is balanced when all the
strengthened; for instance, when the purpose of an
charges made in both the obligations and common
utterance is to provide feedback (e.g. acknowl-
ground have been credited. The current specification
edgments, back-channels, etc.), reinforcing the
of the scheme is presented in tables 1 and 2.
belief of the speaker that the hearer is engaged;
these acts are also normally credited implicitly by
the interlocutor through the normal continuation of
the dialogue. This level also includes explicit non-
participant
understanding signals that the common ground has
been lost (e.g. what did you say?) and needs to be
Finally, ambiguous or vague acts charge the un-
derstanding plane too, but this kind of acts are credited later on when the ambiguity is resolved or
the vague reference is fixed. Also, unlike all other
Table 1. Balancing relations for obligations
common ground act types, ambiguous and vague
charges may be credited by the interlocutor that
made the corresponding charge in the first place.
In the table 1 Action is the act of pointing to an
object, a zone, a path, etc., or the placing, moving or deleting a domain object in the design space. Table
1 also states if a charge is made immediately at the
3. The Transaction’s Structure
time the speech act is performed by the speaker (i.e.
I) or whether it is postponed until it is accepted by
To illustrate this machinery, the analysis of a typical
the hearer (i.e. P). The table also specifies whether
transaction of the DIME Corpus is presented in
the charge is on the hearer or on the speaker
Table 3. The column # stands for utterance number,
T for the turn (System or User), and the numbers in
the charge and credit columns index the utterance
The common ground is defined by agreement acts,
that expressed the corresponding speech acts, for the
related to the shared set of beliefs agreed along the
obligations, agreement and understanding planes
dialogue, and by understanding acts, related to the
communication channel. In normal conversation, it
is assumed that the content of an utterance is
The first utterance in this transaction is an offer
accepted by the interlocutor by default, and most
which creates a charge in the agreement plane, as
forward looking obligation speech acts are accepted
offers need to be accepted or rejected; through
implicitly; however, there are also agreement acts
utterance 2, U accepts the offer, crediting the
that are expressed by explicit speech acts. We have
agreement charge and placing an obligations charge
observed two main cases: (1) the common ground
on S, as the system has now the obligation to
has been broken (e.g. by a referential failure), and
perform the promised action; the main intention of
needs to be repaired, and (2) the common ground is
the transaction is stated in 3 by U; this action
reinforced by the explicit realization of speech acts.
directive places a charge on S in the obligations
The common ground relations are summarized in
plane, and this charge is consistent with the offer
made by S itself in the initial utterance. The action
directive also places a charge in the agreement
Agr-action = {accept | accept-part | hold | maybe |
plane, which is explicitly accepted by S in 4.
Understanding-Act = {acknowledgment | back-
Utterance 5 is an open option made by S; although
channel | repetition | rephrase | complementation |
this type of speech act is normally stated through a
considered an affirm act, as its purpose is not to
Agreement charges are made immediately at the
enrich the set of beliefs of the interlocutor (i.e. to
time the speech act is produced, and are normally
add a proposition in its knowledge base) but simply
credited implicitly by the next utterance produced
to allow him to choose from a predefined set of
by the interlocutor. Understanding dialogue acts
possible courses of action; also, the open option
may express that the common ground needs to be
does not charges the obligation plane, as the inter-
Inteligencia Artificial V. 11, Nº 36, 2007
participant Table 2. Balancing relations for the common ground plane
locutor has no obligation to do anything about it;
are aware that the common ground has been broken
however, the open option does charge the common
and needs to be restored; for this, a problem-solving
ground, as it needs to be accepted or rejected either
process to resolve the referent of the remaining
explicitly or implicitly by the normal flow of the
spatial argument is started. In 10, U answers 9
conversation. Next, U determines further the main
through an affirm act (i.e. here) at the time a spatial
intention through an affirm act in 6, and accepts
zone is pointed at (i.e. the zone corresponding to the
implicitly the open option; although this utterance
far wall). The answer act credits the obligation
has, perhaps, an imperative connotation at the sur-
plane, but the affirm act needs to be accepted and
face level, it is not considered an action directive as
makes a new charge to the agreement level.
its purpose is to make a choice (supported by a
However, the question in 11 expresses that the
pointing act) within the context of the main
spatial reference needs still to be confirmed
transaction’s intention; however, U needs to be sure
(there?); accordingly, and in addition to its
that S took notice, and the affirm act charges the
corresponding charge in the obligations plane, this is
common ground; in 7, S accepts explicitly U’s
also a check question that puts on hold the affirm act
choice, and credits the corresponding charge.
in 10. Theanswer in 12 credits this charge, and U
resolves the spatial ambiguity that he himself had
At this point of the transaction the main intention
introduced in 8, crediting the corresponding charge
(i.e. to place a stove) and one of its arguments (i.e.
in the understanding plane of the common ground
what particular stove) have been fully determined,
but the second argument, the location where the
stove will be placed, is still to be specified. This is
Through 13, S accepts the postponed affirm acts in 8
carried out from utterance 8 to 13. In 8 U states the
and 10, which were uttered by U, making the
desired location through an affirm act, with the
corresponding credits to the understanding plane. At
corresponding charge in the agreement plane;
this point the main intention with its two arguments
however, the statement involves a definite
has been determined, and S is able to commit to do
description (the far wall) which is ambiguous; in the
the action requested by U in 3, making the
2-D and 3-D views (of the interface where the
corresponding charge on himself in the obligations
corpus was collected) there are two walls that can be
plane. This concludes the intention specification
the referent, depending on the position adopted by
the speaker in relation to the working space; for this
reason, 8 charges also the understanding plane with
The satisfaction of the intention involves a problem-
solving process that has the placing of the stove as
its goal; this requires pairing the spatial referent
The spatial ambiguity is noticed by S and utters the
introduced with the pointing action in 10 with a
reference position of the stove (e.g. the center or the
corresponding charge in the obligations plane; this
bottom-left corner), and this involves the use of
question is also a hold act that postpones accepting
some design preferences and constraints adopted by
8 in the common ground. At this point both U and S
the system. Finally, when the plan is decided, the
Inteligencia Artificial V. 11, Nº 36, 2007 Common ground Dialogue Act Types Utterance (originally in Spanish) Table 3. Analysis of a transaction
actual action is performed and expressed through
this question is credited with U’s answer in 16;
the graphical modality. This action credits the
finally, the graphical act is credited in the common
pending offer in 2, the action directive in 3 and the
ground with an accept act expressed by 16 too.
commit in 13 in the obligations plane. The graphical
act makes also an affirm charge in the agreement
Table 3 also illustrates that the structure of the
level, as U needs to agree with the result of this
transaction can be partitioned in two main phases:
action. To conclude the transaction, S makes a
intention specification and intention satisfaction,
and that the kind of speech act is highly dependent
corresponding charge in the obligations plane, and
on the part of the transaction where it occurs; for
Inteligencia Artificial V. 11, Nº 36, 2007
instance, a commit is very likely to occur at the end
is reversed when the common ground is broken, and
of the intention’s specification phase, but very
the acceptance of a speech act is postponed by a
unlikely to occur elsewhere. Also, the main
hold act. In this situation the obligations charges and
intention is very likely to be expressed at the
credits are embedded within the line linking the
beginning of the transaction, and this is made very
charge made by the speech act that was put on hold
often in our corpus through declaratives (more than
with the speech act that finally accepts it and makes
70%) and interrogatives (about 20%); other
the corresponding credit. While in the main
utterances appearing within the context of the main
transaction cycle the conversation’s initiative is held
intention are very unlikely to be action directives,
by U, who imposes obligations on S (in this
unless they appear in embedded transactions. More
particular setting), when the common ground is
generally, the structure of the transaction may be
broken the initiative is shifted to S who guides the
very helpful to interpret direct and indirect speech
conversation in order to reestablish the common
acts, as the interpretation process may be construed
ground; when this is achieved, the conversation’s
as finding the most likely speech act type given the
place in the transaction’s structure in which the
utterance is expressed, taking into account the actual
lexical content and syntactic form of the utterance,
4. Tagging Methodology and Evaluation
Also, unlike written language in which sentences are
produced as ready-made units, intentions in
The presented theory was developed in conjunction
with a transcription task. The exercise started from
incrementally. Although the main intention is
the original DAMSL scheme and its manual [6], and
understood through the meaning of the main verb in
a team that included up to 15 taggers at a time
the interpretation domain and context, working out
participated in the initial training phase. Next, one
the referents of the verbal complements is produced
dialogue was tagged by several people, and the
by an incremental problem-solving process, as
kappa statistics was used to measure agreement
illustrated by the example in Table 3. In this, as in
between taggers [4]. The initial agreement scores
many transactions in our corpus, the accusative
were very low, especially for the common ground
argument is resolved first, followed by the
speech acts and the backwards dimension. One
resolution of other spatial complements.
source of confusion was the implicit assumption that
utterances express speech acts in a context
The transaction in Table 3 does not involve vague
independent fashion, as very few constraints
expressions (e.g. to the left of the stove) where the
between tags are defined in the original DAMSL
spatial information needs to be further determined in
scheme. In fact, the DAMSL manual provides
order to undertake action, which are common in our
explicit decision trees for agreement acts, and
corpus; however, this kind of expressions require
questions in these trees are focused on the function
fixing reference through a problem-solving process
of a particular utterance, independently of its
analogous to the resolution of the ambiguity in the
context in the transaction’s structure.
present example. More generally, the resolution
process for each argument may involve ambiguous
The theory presented in this paper evolved as a
and vague expressions that break the common
reaction to these problems. Dialogues were first
ground, and resolving these, fixing reference and
thought of as sequences of transactions; also, the
restoring the common ground, seem to be three
obligations and common ground were made explicit,
aspects of the same underlying phenomenon.
and the common ground was also explicitly divided
in the agreement and understanding planes of
Finally, Table 3 also shows that the obligations
expression. Then, speech acts were classified
structure ‘dominates’ the common ground in the
according to these structures. In this exercise, the
sense that the dependencies of the latter structure are
DAMSL dimensions (i.e. communicative status,
embedded within the ones of the former. This is
information level and the forward and backward
illustrated by the vertical line linking the statement
looking functions) were preserved, and the
of the main transaction intention with its actual
obligations and common ground structures were
satisfaction, which ‘encloses’ the lines linking
thought of as orthogonal to DAMSL dimensions,
charges with their corresponding credits in the
enriching the level of structure postulated in the
common ground. However this dominance relation
original scheme. The relations between speech acts
Inteligencia Artificial V. 11, Nº 36, 2007
within each plane of expression were modeled in
utterances, and the scheme seems to cover most
terms of the charge and credit import of speech act
phenomena in a simple and consistent way. The
types, and also in relation to the transaction context.
video and audio, with the orthographic transcription,
In addition, as the DIME corpus is multimodal, tags
the charges/credits tagging and the full DIME-
for graphical actions and visual interpretations were
DAMSL annotation of the 20 dialogues is available
In this exercise an Excel format was used to input
the tags for all utterances in a dialogue; this format
5. Conclusion and applications
supported the original DAMSL’s tags and
dimensions as well as the obligations and common
The analysis of speech acts is required in linguistic
ground, and the charges and credits relations. The
studies of discourse and conversation, and also for
format also allowed the semi-automatic computation
the construction of natural language conversational
of the kappa statistics for transaction boundaries,
systems, especially when spoken language is
charge and credits relations and the actual speech
involved. In the present approach, the analysis of
act type tags. Through the exercise a number of
speech acts is partitioned in two levels: the level of
conventions about the interpretation of speech acts
form and the level of content. The level of form is
in relation to the context, and also about the use of
constituted by the obligations and common ground
the tagging tools, were defined and refined. The
structures, and this level is defined in terms of the
relations and constraints between speech acts in the
context of the transaction, and these relations are
With the tagging tool at hand, a formal experiment
independent of the actual beliefs and intentions
involving three tagging teams of three members
expressed by the speech acts. In this sense, the
each was developed. In this exercise two dialogues
obligations and common ground are abstract
from the corpus were transcribed, in a sequence of
structures and hence linguistic generalizations that
tagging rounds; the teams were allowed to comment
are independent of content issues and knowledge
and discuss coincidences and discrepancies at the
end of each tagging cycle and, after a few rounds,
kappa statistics converged up to 0.9 for transaction
The notion of obligations has a long tradition in
boundaries, charge/credits relations and the actual
grammar and logic (e.g. deontic logics), and also in
DIME-DAMSL tags. This figure suggests that the
agreement between taggers above chance is very
consequences of obligation statements that depend
good. At the moment we have 12 dialogues
on syntactic form are studied, but these are not
comprising 139 transactions with 1,702 utterances
tagged with the latest version of the scheme by two
expert taggers (with the exception of charges and
computational linguistics views, in turn, obligations
credits for ambiguous and vague references, which
are commonly defined as goals that arise in
we have only explored in a preliminary way). The
conversation and have to be dealt with in
kappa statistics for this transcription exercise are
conjunction, and some times prior, to the task
shown in Table 4. In addition, the kappa statistics
domain goals of the agent (e.g. [9]). Although in the
for transaction boundaries is 0.83. The current
present approach obligations are also thought of as
results support the case for the theory, and show that
goals that an agent ought to accomplish, these are
the methodology and tagging scheme are reliable.
stated in relation to content independent generic
conversational protocols and, in this sense, the
present view is orthogonal to traditional notions.
The present notion of common ground is also
thought of in terms of structural relations, and in this
respect it resembles Clark and Schaefer’s [5]
Table 4. Kappa stastistics for 1,702 utterances
grounding model; however, unlike this latter model
in which an utterance “presents” a piece of
information that is “accepted” by the next utterance
In addition, one expert tagger has fully tagged 8
additional dialogues and the actual tagged data
2http://leibniz.iimas.unam.mx/~luis/DIME/dimedamsl/CO
comprises 20 dialogues, 269 transactions and 3283
Inteligencia Artificial V. 11, Nº 36, 2007
performed by the interlocutor, forming a grounding
an intention with its arguments is specified
unit, the so-called “contribution”, the present model
incrementally, followed by its satisfaction. In
postulates that there is a set of speech acts that
particular, expressions filling the intention’s
perform specific grounding functions when they are
argument positions are initially understood through
required (avoiding infinite accepting loops). Finally,
meaning, but such expressions have referents which
the explicit demarcation of the obligations and the
need to be resolved, fixed or determined in order to
common ground, with the corresponding constraints
act. The resolution of each of these arguments
and balancing relations, provides for a simple and
becomes embedded subproblems that are also
general model for the analysis of task oriented
solved cooperatively. The resolution of ambiguous
or vague spatial referents, in particular, is an
incremental problem-solving process that is often
The main aim of the present view of dialogue
concluded with an explicit ostension, and this
structure is the construction of conversational
deictic act fixes reference and restores the common
systems in practical dialogues, where a dialogue can
ground at the same time. In this view, anaphoric and
be analyzed as a sequence of task oriented
indexical resolution is subsumed in a process that
transactions. We hold that typical transactions, in
aims to resolve the referents through a problem-
turn, can be modeled through dialogue models
solving process involving conventional meanings,
representing the obligations and common ground
knowledge about the conversational domain, the
structures; in a finite state graph or a recursive
transaction’s structure, and an interaction with the
transition network, for instance, states can represent
conversational situations and arcs the type of speech
acts that relate situations. In this view, navigation
through dialogue models depends on the ability to
Acknowledgments
identify the speech act types expressed by
utterances, taking advantage of the context and,
We thank the support of the people of the DIME
perhaps, prosodic information [7]. We also hold the
group at IIMAS, UNAM; in particular, Patricia
hypothesis that this recognition is mainly a bottom-
Pérez Pavón and Haydé Castellanos. We also
up process; however, when dialogue act types are
acknowledge useful comments by the anonymous
available, issues of content can be addressed in a
reviewers of this paper. The theory and experiment
top-down fashion; for instance, when it has been
reported in this paper are being developed within the
established that an utterance expresses an action
context of the DIME project, with partial support of
directive, lexical and syntactic information could be
used to determine the specific action to be
performed by the system. Also, most common
ground speech acts are interpreted directly, and this
interpretation requires little lexical and syntactic
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