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Processing \hfill{} Juliet Bourne \\ 
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\begin{document}

\mytitle

In this lab a very simple system for introducing the concept of time
into discoursed is shown. It is based on the GPSG context-free grammar
and the lambda calculus semantics used in Lab \#4. Here are the main
features: 

\begin{itemize}
\item Every declarative sentence entered is stamped with the current time.
(The time is simply an integer which is incremented after each
declarative sentence.)
\item Declarative sentences can now have prepositional phrases with
``before'' and ``after''. (Currently, this ability is only given to {\tt
V2} verbs. But it would be easy enough to add this to other verb types.)
\item Yes/No questions involving the relationship in time of two events
in the discourse can be asked using ``before'' and ``after''
prepositional phrases. For example, {\tt Did John see Mary before Bill
laughed}, can be answered. If the time stamp of an event matching the
first clause is less than the time stamp of a match for the second, the
answer will be {\tt Yes}. If one of the clauses does not have a matching
event in the database, the answer will be {\tt I don't think so}.
\item {\tt When} questions can also be asked, for example {\tt When did
John see mary}. If a matching event is found in the discourse database,
it looks for an event with a time stamp that differs by one from this
matched event, with a preference for events that happened after the
matched event.
\item Yes/No questions with prepositional phrases in them can now be
answered accurately. Previously, if the question {\tt Did John see Mary
in the park} was asked, the answer would be {\tt Yes} even if where John
saw Mary was never specified or if the only matching event was {\tt John
saw Mary in the car}. 
\end{itemize}

\noindent Other issues to consider (not implemented):

\begin{itemize}
\item The timing of events should be based on the time stamps as well as
the tense of the verb in the clauses. For example, an event which is in
the past tense entered at time stamp 2 could be considered to have
happened before an event in the present tense at time stamp 1. Exactly
how relate tense and time stamping depends on what the system will be
used for. 
\item When a declarative sentence has a ``before'' or ``after''
prepositional phrase, the event described in the prepositional phrase
should be entered into the discourse database with an appropriate time
stamp. Given the sentence {\tt John saw Mary before Bill laughed}, the
system would answer {\tt Yes} to the question {\tt Did Bill laugh}.
\item Currently, the way responses to {\tt when} questions are answered
is a kludge. It is not possible to obtain the appropriate conjugated
verb from an event frame which only has the root verb and a tense
feature. Thus, instead of saying ``before Bill laughed'' the system says
{\tt BEFORE BILL LAUGH+past}. Some sort of morphological system which
could recover ``laughed'' from the root ``laugh'' and the tense
``past''.
\end{itemize}

\end{document}

