Semantic Analyses and Representations - Man-Machine Dialogue: Design and Challenges - page 77

understand that the user does not want a slow train. In the case of a closed
domain MMD, a fallback strategy would simply be to ignore the
incomprehensible metaphor and only retain the second part of the utterance to
determine the system's reaction.
The phenomena mentioned until now happened at the word level. Yet,
some words such as “reservation” have an additional characteristic: they
allow us to create links with other parts of the utterance. A reservation is
made by someone, the agent, and for something, the object. The identification
of these two actants is necessary to interpret the sentence correctly. Thus
“reservation” has a valency of two, just like the verb “to reserve” does. The
verbal semantics thus rely on this notion of valency, which allows the system
to give a meaning to the prepositions used in the utterance and link the
different components. In “I am reserving a ticket”, the semantics of the verb
“to reserve” thus allows us to determine the agent, “I”, who is also the user,
and the object, a ticket. It is also the case for “I am cancelling my return
reservation”, both for the verb “to cancel”, which has a valency of two, and
for the noun “reservation”, with the possessive form allowing the system to
identify the agent and the complement “return” allows the system to identify
the object. In MMD, the verb identification and its semantics can thus be an
entry point for automatic understanding. Taking valency into account does
not, however, allow the system to link all the components in the sentence.
Thus, in “I am definitely cancelling my return reservation”, and “I am
cancelling my return reservation because I am staying in Paris”, an
unnecessary verb complement is added to give (relevant or irrelevant)
indications on the process application conditions provided by the verb. For
NLP as for MMD, we have to catalog the different verbs with their
characteristics and, while analyzing them, identify the actants expressed as
well as those that are implicit and are thus subject of an ellipsis or a particular
use. There are available dictionaries for the first point, and interpretation
strategies have to be devised for the second.
The fact that some parameters cannot be expressed is at the heart of an
essential phenomenon in language: implicitness. Everything that is not
expressed but that is still carried by the utterance falls within the realm of
implicitness, which thus covers varied phenomena. Among these we can find
ellipses, allusions (“I do not want a snail” can imply “please stop suggesting
trains that are too slow”), presuppositions and other inferences that can be
found through complex pragmatic analysis and not semantic analysis.