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\begin{document}

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\section{Garden Path Sentences}

Adding rules for relative clauses was fairly simple\footnote{Once i
grokked what \verb+create+ and \verb+attach+ do, partly thanks to Chee.}.
In the examples for the lab, it simply meant looking for \verb+who+ or
some noun following a completed \verb+nbar+ node and then creating an
\verb+sbar+ node to be a sister of the \verb+nbar+. Another sentence
node is then created. If \verb+who+ was next, then it looks ahead to see
what follows it. If it is a noun, a \verb+whcomp+ node is attached to
the \verb+s+ node and the appropriate packets for parsing a sentence are
activated. If the word following the \verb+who+ was not a noun, then the
\verb+who+ is treated as the subject and the \verb+major-decl-s+ rule is
called explicitly to parse the sentence. Once the relative clause is
parsed, the \verb+sbar+ is attached to the subject NP of the main
sentence. (See traces.)

With the rules described above, sentences like ``*The boy kissed Sue saw
Bill'' and ``The horse raced past the barn fell'' won't be accepted. The
rules require that there is some sort of explicit subject (an
antecedent, or otherwise) in the relative clause. Without the \verb+who+
or other noun following the \verb+nbar+, the next verb could be either
the main verb or a secondary verb (i.e. for a relative clause). This
problem can be solved with the look-ahead allowed by Marcus' parser.
(See attached code.) When the verb is encountered after the \verb+nbar+
of the subject has the feature \verb+en+ (meaning that it can describe
the state of some object, I suppose, like ``the dog taken to the vet''),
completion of the subject is delayed and the \verb+parse-vp+ is
activated to try to parse a verb phrase. Rules and packets are added to
deal with ending a verb phrase, such that, if another verb immediately
follows a verb phrase that began with a \verb+en+ verb, the verb phrase
just parse will be attach to the subject of the sentence as a
\verb+vpcomp+. Otherwise the parser will fail. (See traces.)

Now here's where I get confused. With the rules I just described above,
the parser can now parse ``The horse raced the barn fell'' as well as
``The horse raced fell'' and ``The newspaper published by the Herald
stank,'' given that both ``raced'' and ``published'' are classified as
\verb+en+ verbs. The \verb+en+-ness of ``raced'' might be questionable,
and making it a non-\verb+en+ verb would solve the problem. (See
traces.) If this is so, the ``garden path'' lies in the semantics of the
sentences, making the first two garden paths and the last one not.
Beyond just the classification of the verbs, richer semantics also
probably come into play, since people know that newspapers are published
and that horses race\footnote{It's not clear that people don't assume
that horses are raced. If they do, then this is not a good explanation
for the classic garden path sentence.}. In the case where ``published''
and ``raced'' are treated the same, then the examples above can be
parsed by Marcus' parser, regardless of whether or not they are garden
path sentences for humans.\footnote{One comment to make about the system
of rules I devised to parse these sentences. As I have it now, the
sentence ``The boy kissed Sue saw Bill'' will also be parsed as
acceptable (even though it is clearly not) if ``kissed'' is classified
as \verb+en+, as in ``the leaves kissed by sunlight''. Here, more
sophisticated verb subcategorization is needed. Speaking semantically,
``leaves'' should be the patient of ``kissed'', not the agent (as my
rules would do now).}

\section{Conjunctions}

For the examples in the lab, creating rules for conjunctions was fairly
easy and straightforward. The easiest case was that of a subject
consisting of conjoined noun phrases. The parser keeps looking for more
of the subject's main noun phrase until a verb is encountered. For
conjoined noun phrases as objects of verbs, it is a bit trickier because
what looks like conjoined noun phrases might be conjoined clauses as in
``Birds eat worms and frogs eat flies.'' The way this is handled is that
if the pattern \verb+conj noun verb+ is encountered\footnote{This has
obvious problems when noun phrases with reduced relative clauses are
being conjoined.}, then the parser ends the noun phrase it was parsing
before the conjunction and starts a new sentence (which gets attached to
a higher \verb+s+ node as a sister of the other \verb+s+ node. (See
traces.)

Adding these simple types of conjunctions was not as easy as adding
conjunctions in GPSG. One problem with Marcus' system is that every type
of conjunction must be handled more or less separately, i.e. you can't
just add rules of the same type to handle every sort of conjunction like
you could in GPSG. However, it should be doable\footnote{Referring to
the sentences to think about: 18 is a prepositional phrase attachment
problem. It could probably be made to work either as high or low
attachment. 19 could be done with little problem, since as key words
such as ``and'' and ``who'' are found, they are attached and the buffer
can take in more words. In this way, where to attach already built
phrases can be determined. 20 is really ambiguous. 21 shouldn't be a
problem, since ``birds and frogs'' is simply the subject of the
question. 22 would probably run into problems with the look-ahead
limitation.}. 


\end{document}
