[CL+NLP Lunch] Reminder: Joint ML+NLP Lunch, Miguel Ballesteros, TODAY @ 12:00pm

[Dallas Card]

Please join us for a special joint ML+NLP lunch at noon today, where
Miguel Ballesteros will be speaking about dependency parsing. Lunch will
be provided!

ML+NLP lunch <http://www.cs.cmu.edu/~nlp-lunch/>
Monday, October 6th at 12:00pm
GHC 6115


Speaker: Miguel Ballesteros, Visiting Lecturer / Postdoc at Universitat
Pompeu Fabra

*Title: Going to the Roots of Dependency Parsing*

In this seminar I will first introduce transition-based dependency parsing
and present the conclusions extracted from a journal paper that I have
never had the chance to present in public, besides I'm going to sum up my
current, past and future research collaboration projects with some new
results and developments.

--

Dependency trees used in syntactic parsing often include a root node
representing a dummy word prefixed or suffixed to the sentence, a device
that is generally considered a mere technical convenience and is tacitly
assumed to have no impact on empirical results. We demonstrate that this
assumption is false and that the accuracy of data-driven dependency
parsers can in fact be sensitive to the existence and placement of the
dummy root node. In particular, we show that a greedy, left-to-right,
arc-eager transition-based parser consistently performs worse when the
dummy root node is placed at the beginning of the sentence (following the
current convention in data-driven dependency parsing) than when it is
placed at the end or omitted completely. Control experiments with an
arc-standard transition-based parser and an arc-factored graph-based
parser reveal no consistent preferences but nevertheless exhibit
considerable variation in results depending on root placement. We conclude
that the treatment of dummy root nodes in data-driven dependency parsing
is an underestimated source of variation in experiments and may also be a
parameter worth tuning for some parsers.


Miguel is a Visiting lecturer - Postdoc in Pompeu Fabra University,
Barcelona, Spain. He works on natural language processing and machine
learning with a special interest on linguistic structure prediction
problems, such as dependency parsing and phrase structure parsing.  He
completed his BsC,  MsC and PhD at the Universidad Complutense de Madrid.
During the last years, he was a Visiting Researcher in Universities of
Uppsala,  Birmingham and Singapore.