clarke@csri.toronto.edu (Jim Clarke) (01/16/89)
AI SEMINAR - Monday, January 30, 11 a.m. in Room SF 3201
(SF = Sandford Fleming Building, 10 King's College Road)
Mark Steedman
University of Pennsylvania
"Combinators and Constituency in Natural Language Understanding"
An applicative system expresses the notions of "application" and
"abstraction" (that is, definition) of concepts represented as
functions. The most familiar example of an applicative system is
the lambda calculus, and many linguistic theories implicitly as-
sume that something like the lambda calculus underlies natural
language syntax. The present paper argues that natural language
syntax is better thought of as the direct reflection of a rather
different kind of applicative system. The systems in question
are based on operations directly related to the simplest combina-
tors of Curry's "Combinatory Logic" -- that is, on variable-free
operators such as functional composition, rather than on the
bound variables and variable-binding operator of the lambda cal-
culus. It seems reasonable to think that the same considerations
which have motivated certain recent proposals to use combinators
in compilers and interpreters for functional program- ming
languages may also be at work in forcing natural languages to
take this form.
The main consequence of the approach is to dramatically general-
ise the concept of surface structure and constituency in natural
language. Its benefits lie in providing a very simple account of
coordinate constructions and unbounded dependencies in natural
languages. Coordinate constructions (and other phenomena which
give rise to non-standard fragmentary constituents) currently
pose grave problems for computational applications. The conse-
quences of the theory for processing written and spoken natural
language are considered.
--
Jim Clarke -- Dept. of Computer Science, Univ. of Toronto, Canada M5S 1A4
(416) 978-4058
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