On the role of lexical features in sequence labeling Conference Paper uri icon

abstract

  • We use the technique of SVM anchoring to demonstrate that lexical features extracted from a training corpus are not necessary to obtain state of the art results on tasks such as Named Entity Recognition and Chunk- ing. While standard models require as many as 100K distinct features, we derive models with as little as 1K features that perform as well or better on different do- mains. These robust reduced models in- dicate that the way rare lexical features contribute to classification in NLP is not fully understood. Contrastive error analy- sis (with and without lexical features) in- dicates that lexical features do contribute to resolving some semantic and complex syntactic ambiguities - but we find this contribution does not generalize outside the training corpus. As a general strat- egy, we believe lexical features should not be directly derived from a training corpus but instead, carefully inferred and selected from other sources.

publication date

  • January 1, 2009