[Prev][Next][Index]

Xtag Meeting on April 29: Laura Kallmeyer will be talking this Thursday during the Xtag slot.

We are using the Xtag meeting slot for Laura Kallmeyer's talk this
Thursday. Laura is a visiting researcher at IRCS from the University of
Tubingen. 

Rashmi

---------------------------------------------------------------------

Time: 10:30 - 12:00
Where: Room #413, IRCS (Back conference room)

----------------------------------------------------------------------

                     Tree Description Grammars 
                                and 
                    Underspecified Representations

                           Laura Kallmeyer

Abstract:

In this talk, I will speak about (local) Tree Description Grammar (TDG),
a grammar formalism I have developed in my PhD thesis. TDGs bring
together some of the central ideas in the context of Tree Adjoining
Grammars (TAG) on the one hand, and approaches to underspecified
semantics for scope ambiguities on the other hand.

Starting with Vijay-Shanker 1992, several variants and extensions of
TAGs have been proposed that deal with tree descriptions (i.e. logical
formulas) instead of trees (i.e. structures). Descriptions lead to
underspecification in a very natural way. Approaches in the context of
underspecified semantics that deal with scope ambiguities have the
common property that they all use a partial order to represent scope.
For scope ambiguities, this partial order is not fully specified.
Connecting these two ideas, I define (local) TDGs, a grammar
consisting of tree descriptions that has some of the nice properties of
TAGs and that allows the generation of underspecified representations
for scope ambiguities.

First a general definition of TDGs is presented, and afterwards a
restricted variant called local TDGs is proposed. Since the elements of
a local TDG are tree descriptions, an extended domain of locality as in
TAGs is provided by this formalism. Consequently, local TDGs can be
lexicalized, and local dependencies such as filler gap dependencies can
be expressed in the descriptions occurring in the grammar.
  
The tree descriptions generated by local TDGs are such that the
dominance relation (the reflexive and transitive closure of the parent
relation) need not be fully specified. Dominance is a partial order and
can be used to represent scope relations. Therefore the generation of
suitable underspecified representations for scope ambiguities is
possible with (local) TDGs.

The generative capacity of local TDGs is greater than the one of TAGs.
Local TDGs are even more powerful than set-local multicomponent TAGs
(MC-TAG). However, the generative capacity of local TDGs is restricted
in such a way that only semilinear languages are generated. Therefore
these languages are of constant growth, a property generally ascribed to
natural languages.
  
In order to describe the relation between two languages, in particular
the relation between syntax and semantics, I introduce synchronous local
TDGs. The synchronization with a second local TDG does not increase the
generative power of the grammar in the sense that each language
generated by a local TDG that is part of a synchronous pair of local
TDGs, also can be generated by a single local TDG. Using synchronous
local TDGs, I illustrate the derivation of underspecified
representations for quantifier scope ambiguities with local TDGs.

--------------------------------------------------------------------