Reference Resolution - Man-Machine Dialogue: Design and Challenges - page 108

As for the reference, the anaphora and coreference can refer either to
concrete objects or to abstract objects, and especially events. In “the
reservation failed, I did not get a ticket”, there is a link between the
reservation's progress and receiving a ticket. In “I have reserved a
single ticket for Paris with a specific time and seat. I will start again with a
single ticket for Lyon”, the verbal phrase “to start again” can only be
understood with the antecedent that clarifies the reservation. Finally, an
example of event coreference within the frame of our favorite task is the
following: “I am reserving a ticket for Paris. I would like a single”. In all
these examples, the MMD system is confronted with two sentences or two
propositions that both describe an event, and that are linked to one another.
The link depends on the nature of the events and their representation in a
conceptual model. Thus, getting a ticket can be considered as the last
constitutive step of a reservation. The challenges for an MMD system are
multiple in this case: it first has to determine the anaphoric or coreferring
link, then to link the semantic contents of both sentences using this link and
then to infer a semantic content that could cover both sentences, or if that is
impossible, to clarify the type of discourse relation that exists between them.
These are the key aspects to understanding, which allows the system to
approach a dialogue's coherence with efficiency, but involves many pieces of
knowledge that are hard to implement. In the case of the first example, the
second sentence “I did not get a ticket” explains the observation made in the
first sentence. To identify this discourse relation, the system has to understand
not only the link between both events but also that the user is expressing
his/her problem with a reasoned description. The system can thus refute the
link by answering “the reservation succeeded but the ticket was sent to you
yesterday and will only arrive tomorrow”. In the case of the second example,
the semantics of the verbal phrase “to start again” allows the system to start a
new reservation by using all the settings of the old reservation except that the
destination is clarified. In the case of the third example, the two events are
simply one and the same (but this has to be understood first), which allows the
system to define a query with all the settings, those mentioned in the first
sentence and those mentioned in the second sentence.
As we can see, reference is indeed a pragmatic question that goes beyond
the simple identification of a referent: with the notion of reference domain,
with the use of dialogue history and the links that are drawn between the
different modalities and with the notions of coreference and coherence, it
appears to be a complex mechanism that contributes to the dialogue's
coherence.