Reranking Parse Trees with a SRL system

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Reranking Parse Trees with a SRL system

• Charles Sutton and Andrew McCallum
• University of Massachusetts
• June 30, 2005

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Motivation for Joint Processing
VERB barked ARG0 the dog ARG1 the man AM-LOC
TV

• Miller (2000) single probabilistic model for
  parsing, relations
• Why not for SRL?
• Rather than augmenting grammar, we use reranking
  approach

Long-range features
Uncertainty
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Reranking by weighted combination
Basic MaxEnt SRL model

• Rerank n-best parse trees from Bikels
  implementation of Collins parser
• Gildea Jurafsky tried this with ?0.5

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Weighted combination
Choosing tree by SRL score has lower recall
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Training a global reranker

• MaxEnt reranking of parse tree list, using
  features from base SRL frame
• Inspired by Toutanova et al. 2005, but different.

• Features include
• Standard local SRL features
• Does arg Ax occur in frame?
• Linear sequence of frame arugments (e.g.
  A0_V_A1)
• Conjunctions of heads from argument pairs
• Parse tree score

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Ceiling performance
Best SRL performance of parse-tree reranking
system.
Parse F1 95.0
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Discussion / Future Work

• Reranking parse trees has strong limitations
• Marginalizing over parse trees
• Should SRL / parsing be joint at all?
• If not, how different than MUC relation
  extraction?
• (Miller et al., 2000)