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XTAG meeting on July 6, 10:30am: Seth's Defense Practice Talk


Seth Kulick will give a practice talk for his Dissertation defense:

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Constraining Non-Local Dependencies in Tree Adjoining Grammar:
       Computational and Linguistic Perspectives
		- Seth Kulick


Tree Adjoining Grammar (TAG) is an appealing formalism for the
representation of natural language syntax for both its linguistic and
computational properties.  It forces the substantive theory of syntax to
be stated over small structural domains, the "elementary trees", and
various syntactic locality constraints fall out from the restricted nature
of a TAG derivation.  Being a "mildly context-sensitive"  formalism, it
can also derive some linguistically significant formal languages, such as
the copy language.

An important problem arises, however, when considering languages such
asSpanish or German, which have unbounded dependencies of a different sort
than those found in English.  Such so-called "reduced constructions" as
clitic-climbing (Spanish) or long scrambling (German) have been used to
argue for modifications of TAG that abandon the notion of locality in a
TAG derivation, with both linguistic and formal consequences.

In this thesis we argue instead that the reduced constructions can be
analyzed within a TAG framework without sacrificing the desirable
linguistic and mathematical properties.  A closer examination of the core
cases of unbounded dependencies reveals an underlying structural problem
for TAG, of which the reduced constructions can be seen as one particular
case.  The reduced constructions therefore help point the way towards a
natural revision of TAG, Segmented TAG (SegTAG).

Since SegTAG has the same notion of derivational locality as TAG, we not
only retain but extend TAG's approach to syntactic locality violations to
include cases of unacceptable reduced constructions.  We also show how the
cross-linguistic differences in clitic climbing and long scrambling can be
reduced to the difference in their morphological representation in an
elementary tree.  SegTAG is able to retain TAG's derivation of
cross-serial dependencies and the copy language, unlike some other
extensions of TAG.

Interesting questions are raised about the competence/performance
distinction.  Locality is retained in this system by sacrificing coverage
of some theoretically possible cases of long scrambling that never
actually occur, due to their excessive complexity.  While such cases are
usually ruled out by performance considerations, this work shows that such
cases can instead fall outside the competence grammar itself.  Due to the
context-free nature of a SegTAG derivation, there is a close connection
between the phrase structure of an elementary tree and the range of long
scrambling sentences that can be derived.

We also show how formalisms in the TAG framework are different (perhaps
uniquely so) from other grammar formalisms in how the aspects of reduced
constructions other than clitic climbing and long scrambling must be
analyzed. In some ways the challenges posed for TAG by these other cases
are actually more severe.  We investigate in detail how one such
construction, the Spanish long reflexive passive, can be analyzed in TAG.

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