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Reranking Parse Trees with a SRL system

Reranking Parse Trees with a SRL system. Charles Sutton and Andrew McCallum University of Massachusetts June 30, 2005. Motivation for Joint Processing. VERB : barked ARG0 : the dog ARG1 : the man AM-LOC : TV. Miller (2000): single probabilistic model for parsing, relations

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Reranking Parse Trees with a SRL system

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  1. Reranking Parse Trees with a SRL system Charles Sutton and Andrew McCallum University of Massachusetts June 30, 2005

  2. 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

  3. Reranking by weighted combination Basic MaxEnt SRL model • Rerank n-best parse trees from Bikel’s implementation of Collins parser • Gildea & Jurafsky tried this with =0.5

  4. Weighted combination Choosing tree by SRL score has lower recall

  5. 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

  6. Ceiling performance Best SRL performance of parse-tree reranking system. Parse F1: 95.0

  7. 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)

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