\mysection{The Design of the Interchange Format (IF)}
\label{irf}

Although {\sc Nespole!} will include multiple translation engines, the
showcase systems will focus on translation via an interlingua.
Analysis modules map source language utterances onto the interlingua
representation, and generation modules map interlingua representations
onto target language utterances.  The interlingua represents the
meaning of the source language utterance independently from how it is
expressed in the grammar of the source language \cite{nirenburg:92}.
Interlingua systems are efficient for multi-lingual situations because
one interlingua representation can be input to several target language
generators simultaneously, thus avoiding the need for a different set
of transfer rules between each source-target pair.

The Interchange Format corresponds to Workpackage~4 (Intermediate
Representation Format) in our partners' European proposal.  Carnegie
Mellon will be the leader of this workpackage, with participation from
IRST, CLIPS, and UKA on interlingua design and participation from APT
and AETHRA on domain-specific content.

\paragraph{History of the Interchange Format:}
The {\sc Nespole!} interlingua is called Interchange Format (IF), and
originated in the C-STAR Consortium in 1997.  It has been used since
then in translation of task-oriented dialogues in the travel domain in
six languages (English, French, German, Italian, Japanese, and
Korean), thus demonstrating usefulness in different language families.
There is a database of 4423 utterances, sampled from five languages,
labelled with IF representations.  Intercoder agreement for assigning
IF representations has not been checked, but translation success among
different C-STAR partners shows that the various C-STAR partners use it
consistently with each other.  IF can not only serve {\sc Nespole!}'s
translation needs, but can be a resource to other projects working
with multilingual data.  

%% We need to add Hindi to C-STAR so that we have languages starting
%% with E, F, G, H, I, J, K. :)	

\paragraph{Balancing robustness and expressive power in task-oriented
and descriptive sentences:} The interlingua is the medium through
which analysis and generation modules communicate; therefore it
determines the set of all and only the meanings which are to be made
available through translation.  It should therefore be rich in order
to support expressivity.  However, if the interlingua is too complex,
we risk failure in not being able to produce it reliably.  Robustness
is often pursued by giving up full expressivity (as it was in our
previous work \cite{icslp-98}), with the consequence that parts of the
information content of the input are kept out of the reach of the
interlingua.  Building on previous experience, we intend to provide
for an interlingua which optimally balances such conflicting
requirements, at the same time effectively contributing to the goals
of scalability and cross-domain portability.

In balancing the conflicting requirements on the interlingua, it is
important to distinguish between task-oriented utterances and
descriptive utterances.  Our previous work dealt only with
task-oriented utterances --- those which involve speech acts such as
suggestions ({\it How about a double room\/}), requests ({\it Could
you make that reservation for me\/}), acceptances ({\it A double room
will be fine\/}), etc. Translation of a task-oriented utterances
focuses mainly on the speech act and not very much so on literal
translation of the words.  In fact, task-oriented sentences often
cannot be translated literally.  Descriptive utterances, on the other
hand, convey mainly semantic content and are less distinguished from
each other on the basis of speech act. Examples of descriptive
utterances in the {\sc Nespole!} domains are {\it The castle was built
in the thirteenth century\/} or {\it When I turned it on, nothing
happened\/}.

\paragraph{Description of IF:}
In the treatment of task-oriented sentences, IF uses the concept of
{\it domain actions\/} such as requesting information about the
availability of a hotel or giving information about the price of a
tour.  Each domain action consists of a speech act such as {\tt
request-information} or {\tt give-information}, optionally some
concepts such as {\tt availability} or {\tt price}, and optionally
some arguments with values such as {\tt double room} or {\tt one
hundred dollars per night}.  The IF specification document includes 44
speech acts and 93 concepts, and 117 argument names, although not all
combinations of these are used.  The IF database of 4423 sentences
contains 554 distinct combinations of speech acts and concepts.
However, the current English analysis and generation grammars are
designed to recognize and generate many more (around 3000) domain
actions.  The following examples illustrate some typical uses of IF.  

\begin{small}
\noindent
no that's not necessary\\
{\tt negate}

\noindent
and i was wondering what you have 
in the way of rooms available during that time\\
{\tt request-information+availability+room}

\noindent
and how will you be paying for this\\
{\tt request-information+payment (method=question)}

\noindent
however the rate for the double is one thirty four ninety five per night\\
{\tt a:give-information+price+room
(room-type=double, price=(quantity=134.95, per-unit=night))}

\noindent
i+m now arriving june sixth\\
{\tt c:give-information+temporal+arrival (who=I, time=(june, md6))}
\end{small}

\paragraph{Strengths of the IF representation:}
{\it Multilinguality:} IF is suitable for multilingual situations
because it retains nothing from the source language grammar, but
represents only the speaker's domain action.  This type of interchange
format is desirable for task-oriented sentences whose surface
expression varies greatly among languages.

{\it Suitability for many analysis methods:} Another advantage of IF
is that it is well suited for knowledge-based parsing (\cite{amta-98})
as robust analysis methods which attempt to extract domain actions
without a detailed analysis of each sentence \cite{marcus:99,fukada}.

{\it Scalability and Portability:} The speech act portion of an IF
representation is domain-independent, as are many of the arguments
such as {\tt time} and {\tt quantity}.  Extending IF for a new domain
involves identifying domain-specific concepts and arguments, which can
be done efficiently with corpus-based methods.

\paragraph{Plans for extending IF:}
In order to accommodate descriptive utterances in {\sc Nespole!}, we
will add an interlingual representation of propositional content
(\cite{dorr-book}) using an ontology of concepts (e.g.,
\cite{goodman:91}).  We plan to address the following research issues:

{\it Treatment of translation mismatches:} Speech-act-based
interlinguas explicitly address the problem of translation mismatches
--- instances where a literal translation does not work --- which
arise frequently in task-oriented sentences.  However, translation
mismatches also arise in descriptive sentences and have been widely
studied (e.g., \cite{dorr-mismatch}).  It is our feeling that many
mismatches in descriptive sentences can be attributed to the way that
closed class meanings are expressed (e.g., tense, aspect, certainty,
ability, obligation, and evidentiality) \cite{levin+nirenburg}.  Our
work will address the representation of closed class meanings in order
to assure high quality translation in the case of translation
mismatches.

{\it Representation of topic and focus:} Another point that must be
addressed concerns information-packaging, in particular the
representation of {\it topic\/} (given information) and a {\it
focus\/} (new information) (e.g., \cite{comrie}).  Capturing such
information in a grammar-independent representation is crucial because
languages have different grammatical means to realize topic-focus.  Even
in the task-oriented representation of domain actions, the topic/focus
distinction is necessary to distinguish {\it The Hilton Hotel is in
Verona\/} where {\it The Hilton Hotel\/} is topic from {\it The hotel
in Verona is the Hilton Hotel\/} where {\it The Hilton Hotel\/} is
focus.

{\it Representation of multimodal information in IF:}
Finally, in the {\sc Nespole!} project IF plays the important role of
providing the symbolic level encoding of multimodal links between
linguistic referential items and their pictorial/visual referents.

%% \paragraph{Milestones:}
%% Milestones include (1) the first version of the task-oriented IF for
%% the expanded tourist domain (end of Year~1); (2) the first version of
%% the descriptive-oriented IF for the expanded tourist domain (Year~2);
%% (3) representation of multimodal information and synchronization of
%% verbal and non-verbal information (Year~2); (4) the adaptation of the
%% task-oriented IF for the help-desk domain (Year~2); and (5) the
%% adaptation of the descriptive-oriented IF for the help desk domain
%% (Year~3).






