Negation is a pervasive phenomenon in natural language, occurring in every language and every genre. Despite the obviously profound impact of negation on the meaning of a sentence, the most common approach to handling negation in NLP systems is to ignore it, leading to all manner of (frequently) comical errors. To encourage the exploration of better solutions, the 2012 *SEM Shared Task focused (among other things) on automatically identifying negation and determining its scope. Several of the resulting systems were quite successful, but despite the semantic nature of the task, the vast majority of them were based on surface or syntactic methods.
In this talk, we will describe a semantics-based method of attacking the same problem. Our system is based on the Minimal Recursion Semantics structures produced by the English Resource Grammar, a broad-coverage, precision, computational HPSG account of English. We show that it is relatively straightforward to design high precision rules to determine what portion of a sentence is within the scope of negation, by "crawling" through these graphs. In a system combination with the winner of the 2012 competition, our method yields improved precision and F1. Moreover, our "crawling" rules can be seen as a first-pass formalization of the shared task annotation guidelines.
Woodley Packard is currently a CLMS student at the University of Washington. Since completing his M.S. and B.S. in Mathematics at Stanford University in 2006, he spent three years at a web technology startup, and has also spent time at the University of Oslo in Norway. He is also the author of the ACE parser-generator and various other experimental NLP tools.
Emily M. Bender is an Associate Professor of Linguistics and Adjunct Associate Professor of Computer Science and Engineering at the University of Washington. She is the Faculty Director of UW's Professional Masters Program in Computational Linguistics (CLMS). Her research interests center on multilingual grammar engineering, computational semantics, and the relationship between linguistics and computational linguistics. Her book, _Linguistic Fundamentals for Natural Language Processing: 100 Essentials from Morphology and Syntax_ appeared this year in Morgan & Claypool's Synthesis Lectures in Human Language Technologies.