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Tree Edit Models for Recognizing Textual Entailments, Paraphrases, and Answers to Questions Michael Heilman and Noah A. Smith lti Summary Simple transformational approach for modeling sentence pair relations. Experiments for

  1. Tree Edit Models for Recognizing Textual Entailments, Paraphrases, and Answers to Questions Michael Heilman and Noah A. Smith lti �

  2. Summary � Simple transformational approach for modeling sentence pair relations. � Experiments for multiple problems: • Recognizing textual entailment • Paraphrase identification • Paraphrase identification • Answer selection for question answering � Competitive but not standout performance. lti �

  3. Intuition Tree edits are syntactic transformations that can modify semantic properties in various ways. oblique oblique pp-obj. pp-obj. subj. Before1848 L.A. belonged to Mexico Canada before1848 We represent sentence pairs as sequences of edits that convert one tree into the other. lti �

  4. Outline � Introduction � Connections to Prior Work � Finding & Classifying Edit Sequences � Experiments lti �

  5. Prior Work on Sentence Pairs � Numerous approaches for sentence pair relations, some task-specific. � Considerable work involving tree and phrase alignments. Das & Smith, 09; MacCartney et al., 08; Zanzotto, 09; Chang et al., NAACL-10; inter alia � Less work on transformational or tree edit approaches. Harmeling, 07; Bar Haim et al., 07 lti �

  6. Prior Work on Tree Edit Distance 1. Local edits without reordering. insert, relabel, delete • 2. No learning of associations between labels and features of edit sequences. Chawathe et al., 97; Punyakanok et al., 04; Wan et al., 06; Bernard et al., 08; inter alia lti �

  7. Our Method 1. Includes edits for reordering children and moving subtrees. 2. Learns associations between edit sequences and features of labeled data. 3. Does not require: 3. Does not require: WordNet • Distributional Similarity • Possible NER • future work Heavy task-specific tuning • Coreference resolution • Etc. • lti �

  8. Outline � Introduction � Connections to Prior Work � Finding & Classifying Edit Sequences � Experiments lti �

  9. With a wry smile, Mr. Bush replied, “You're looking pretty young these days.” Bush shot back: “You're looking pretty young these days.” DELETE ( a ) θ θ Feature Value DELETE ( wry ) # edits # edits 8 8 DELETE ( smile ) DELETE ( smile ) DELETE ( with ) # unedited nodes 11 RELABEL ( replied , shot ) # DELETE 5 DELETE ( Mr. ) # INSERT 1 INSERT ( back , shot ) # delete subject 0 RELABEL ( comma , : ) … PARAPHRASE lti �

  10. Types of Tree Edits � Inserting, Deleting, MOVE-SIBLING Relabeling Nodes INSERT-CHILD Socrates taught to Plato philosophy. • INSERT-PARENT • DELETE-LEAF • Socrates taught philosophy to Plato. DELETE-AND-MERGE • RELABEL-NODE • RELABEL-EDGE • MOVE-SUBTREE � Reordering Children MOVE-SIBLING I saw the man with the telescope • � Moving Subtrees MOVE-SUBTREE • I saw the man with the telescope NEW-ROOT • lti ��

  11. Complexity � Tree edit distance with insert, relabel, delete edits: O( n 3 log n ) Klein, 98 � With reordering and moving subtrees: Polynominal runtime algorithms not available lti ��

  12. Greedy Best-First Search � We choose the next tree according to the heuristic function only. Pearl, 84 • We ignore path cost. Target Tree Target Tree (e.g., hypothesis) Initial Tree (e.g., premise) ��

  13. Tree Kernel Search Heuristic � Heuristic compares current tree to target tree ( ). � Tree kernel : similarity measure between trees based on similarities of all their subtrees. • Efficient dynamic programming solution. D. Haussler, 99; Collins & Duffy, 01; Zanzotto & Moschitti, 06; Zelenko et al., 06 ��

  14. Tree Kernel Search Heuristic � In general, larger trees will have larger kernel values. � So we “normalize” to [0, 1]: ( ( , , ) ) K K X X X X ( ( ) ) 1 1 = = − − H H X X ( , ) ( , ) × K X X K X X heuristic tree kernel function function ��

  15. Finding Edit Sequences � Operations are very expressive. • Search rarely fails (< 0.5%). � Resulting sequences: • Succinct and plausible upon inspection • Succinct and plausible upon inspection • Internally consistent representation • Lead to good performance lti ��

  16. Example Edit Sequence Premise Hypothesis lti ��

  17. Example Edit Sequence RELABEL-NODE(nearby) MOVE-SUBTREE(Blvd.) MOVE-SUBTREE(Pierce) Multiple RELABEL-EDGE, DELETE-LEAF, DELETE- AND-MERGE edits lti ��

  18. Classifying by Edit Sequences � Logistic Regression with 33 features. • total number of edits • number of X edits • number of edits removing a subject • number of unedited nodes • etc. etc. � We learn separate parameters for each task from labeled sentence pairs. lti ��

  19. Outline � Introduction � Connections to Prior Work � Finding & Classifying Edit Sequences � Experiments lti ��

  20. Recognizing Textual Entailment Challenge: Decide whether a hypothesis follows from a premise. � Testing: RTE-3 test data. Giampiccolo et al., 07 � Training: RTE-3 dev. data and data from � Training: RTE-3 dev. data and data from previous RTE tasks. lti ��

  21. RTE-3 Results de Marneffe et al. 06 80 75 Syntactic alignment + Accuracy (%) classification 70 Tree edit model 65 MacCartney & Manning 60 08: Hybrid 08: Hybrid 55 de Marneffe et al. 06 50 + Natural Logic technique ��

  22. Paraphrase Identification Challenge: Decide whether 2 sentences are paraphrases of each other. � Paraphrase ≈ bidirectional entailment. � Microsoft Research Paraphrase Corpus � Microsoft Research Paraphrase Corpus � Standard training and testing splits Dolan et al., 04 lti ��

  23. Paraphrase Identification Results Tree edit model 80 Wan et al. 06 75 Accuracy (%) SVM with syntactic 70 dependency overlap, 65 BLEU scores, tree edit 60 distance, etc. distance, etc. A Das & Smith 09 55 Quasi-synchronous 50 Grammar to model syntactic alignments + n-gram overlap ��

  24. Answer Selection for QA Challenge: rank sentences by correctness as answers to a given question. � We find edit sequences from answers to questions. � We rank by the estimated probabilities of correctness. ��

  25. Answer Selection Data � Q&A pairs from TREC-8 through TREC-13. � Training, Dev., Testing data sets: about 100 questions and 500-1500 answers each lti ��

  26. Answer Selection Results Punyakanok et al. 04 0.75 an Average Precision) Tree edit distance 0.65 Ranking Quality Wang et al. 07 0.55 Quasi-synchronous 0.45 Grammar to model syntactic alignments syntactic alignments R (Mean 0.35 0.35 Wang et al. 07 + WN 0.25 plus lexical semantics from WordNet Tree edit model ��

  27. Answer Selection Results Punyakanok et al. 04 0.75 an Average Precision) Tree edit distance 0.65 Ranking Quality Wang et al. 07 0.55 Quasi-synchronous 0.45 Grammar to model syntactic alignments syntactic alignments R (Mean 0.35 0.35 Wang et al. 07 + WN 0.25 plus lexical semantics from WordNet Tree edit model ��

  28. Answer Selection Results Punyakanok et al. 04 0.75 an Average Precision) Tree edit distance 0.65 Ranking Quality Wang et al. 07 0.55 Quasi-synchronous 0.45 Grammar to model syntactic alignments syntactic alignments R (Mean 0.35 0.35 Wang et al. 07 + WN 0.25 plus lexical semantics from WordNet Tree edit model ��

  29. Conclusions Syntax-based tree edit algorithm for classifying sentence pairs according to semantic relationships. � Expressive : includes tree edits for reordering and moving subtrees. reordering and moving subtrees. � Data Driven : learns parameters from labeled examples. � Useful for various tasks lti ��

  30. lti ��

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