UTCS Colloquium/AI: Johan Bos University of Rome La Sapienza: Robust Computational Semantics ACES 2.402 Thursday January 18 2008 11:00 a.m.

Contact Name: 
Jenna Whitney
Date: 
Jan 18, 2008 11:00am - 12:00pm

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Type of Talk: UTCS Colloquium/AI

Speaker Name/Affiliation: Jo

han Bos/University of Rome La Sapienza

Date/Time: Friday January 1

8 2008 11:00 a.m.

Host: Vladimir Lifschitz

Talk Title: Ro

bust Computational Semantics

Formal methods for the analysis of the

meaning of natural
language expressions have long been restricted to the
ivory
tower built by semanticists logicians and philosophers of
la

nguage. It is only in exceptional cases that they make their
way straigh

t into natural language processing tools. Recently
this situation has c

hanged. Thanks to the development of
treebanks (large collections of tex

ts annotated with syntactic
structures) robust statistical parsers trai

ned on such
treebanks and the development of large-scale semantic lexic

a
we now have at our disposal systems that are able to produce
forma

l semantic representations achieving very high coverage.
Even only a few
years ago this was pure fantasy. This is an
interesting development (an

d result) and shouldn''t be left
unnoticed. It makes formal semantics ac

cessible to practical
natural language processing and opens the door to
using
inference tools developed in the area of automated deduction

such as theorem provers and model builders for first-order
logic. Most o

f all it identifies potential gaps between theory
and practice and for

ces the computational semanticist to
transfer theoretical ideas develope

d in isolation into one
unifying framework aiming at covering a wide var

iety of
semantic phenomena.

In this talk I present such a system

developed by myself over
the last three years. This system Boxer imple

ments Discourse
Representation Theory (DRT) a formal theory of meaning
with
the help of Combinatory Categorial Grammar (CCG) for producing

syntactic structure and a typed lambda calculus to specify the
syntax-s

emantics interface. In conjunction with a robust CCG
parser Boxer achie

ves very high coverage on newswire text
producing first-order representa

tions that can directly feed
into standard automated theorem provers. Th

e existence of Boxer
is clear evidence that practicing semantics is not

bound to
pencil and paper exercises anymore nor to implementations
c

overing only baby fragments of English.

Overall from the perspectiv

e of computational semantics this
is good news. It demonstrates that we
have made substantial
progress. But Boxer however impressive it may be
has many
shortcomings too. Modelling all nuances of meaning is an
i

mmense task --- perhaps even impossible --- and what Boxer
does as any

rival system is only produce an approximation of
the meaning of an inpu

t text. An interesting question to ask
then is how good this approximati

on is. How do we access the
semantic adaquacy of systems like Boxer that
claim to be able
to compute meaning?

Speaker Bio:
Johan Bos g

ot his first degree in Computational Linguistics
from the University of

Groningen in 1993. He then moved on to
Saarbruecken Germany and comple

ted his PhD there in 2001.
After that he took up a post-doc position at

the University of
Edinburgh at the Informatics Department. He is current

ly
enjoying a fellowship funded by the Italian ministry and since
200

5 based at the University of Rome La Sapienza. His
research interests c

omprise almost all aspects of natural
language processing in particula

r those that concern
semantics.