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Viterbi Training Improves Unsupervised Dependency Parsing Valentin I. Spitkovsky with Hiyan Alshawi (Google Inc.) Daniel Jurafsky (Stanford University) and Christopher D. Manning (Stanford University) Spitkovsky et al. (Stanford & Google)


  1. The Problem Learning Learning: EM, via inside-outside re-estimation sentences { s } , legal parse trees t ∈ T ( s ) Spitkovsky et al. (Stanford & Google) Viterbi EM CoNLL (2010-07-15) 7 / 26

  2. The Problem Learning Learning: EM, via inside-outside re-estimation sentences { s } , legal parse trees t ∈ T ( s ) , and a gold t ∗ Spitkovsky et al. (Stanford & Google) Viterbi EM CoNLL (2010-07-15) 7 / 26

  3. The Problem Learning Learning: EM, via inside-outside re-estimation sentences { s } , legal parse trees t ∈ T ( s ) , and a gold t ∗ non-convex objective — very sensitive to initialization Spitkovsky et al. (Stanford & Google) Viterbi EM CoNLL (2010-07-15) 7 / 26

  4. The Problem Learning Learning: EM, via inside-outside re-estimation sentences { s } , legal parse trees t ∈ T ( s ) , and a gold t ∗ non-convex objective — very sensitive to initialization maximizing the probability of data (sentence strings): � � ˆ θ UNS = arg max P θ ( t ) θ s t ∈ T ( s ) � �� � P θ ( s ) Spitkovsky et al. (Stanford & Google) Viterbi EM CoNLL (2010-07-15) 7 / 26

  5. The Problem Learning Learning: EM, via inside-outside re-estimation sentences { s } , legal parse trees t ∈ T ( s ) , and a gold t ∗ non-convex objective — very sensitive to initialization maximizing the probability of data (sentence strings): � � ˆ θ UNS = arg max P θ ( t ) θ s t ∈ T ( s ) � �� � P θ ( s ) supervised objective would be convex (counting): � ˆ P θ ( t ∗ ( s )) θ SUP = arg max θ s Spitkovsky et al. (Stanford & Google) Viterbi EM CoNLL (2010-07-15) 7 / 26

  6. The Data WSJ Standard Corpus: WSJ k Spitkovsky et al. (Stanford & Google) Viterbi EM CoNLL (2010-07-15) 8 / 26

  7. The Data WSJ Standard Corpus: WSJ k The Wall Street Journal section of the Penn Treebank Project (Marcus et al., 1993) Spitkovsky et al. (Stanford & Google) Viterbi EM CoNLL (2010-07-15) 8 / 26

  8. The Data WSJ Standard Corpus: WSJ k The Wall Street Journal section of the Penn Treebank Project (Marcus et al., 1993) ◮ ... stripped of punctuation, etc. Spitkovsky et al. (Stanford & Google) Viterbi EM CoNLL (2010-07-15) 8 / 26

  9. The Data WSJ Standard Corpus: WSJ k The Wall Street Journal section of the Penn Treebank Project (Marcus et al., 1993) ◮ ... stripped of punctuation, etc. ◮ ... rid of sentences left with more than k POS tags; Spitkovsky et al. (Stanford & Google) Viterbi EM CoNLL (2010-07-15) 8 / 26

  10. The Data WSJ Standard Corpus: WSJ k The Wall Street Journal section of the Penn Treebank Project (Marcus et al., 1993) ◮ ... stripped of punctuation, etc. ◮ ... rid of sentences left with more than k POS tags; ◮ ... and converted to reference dependencies — { t ∗ } , using “head percolation rules” (Collins, 1999) . Spitkovsky et al. (Stanford & Google) Viterbi EM CoNLL (2010-07-15) 8 / 26

  11. The Data WSJ Standard Corpus: WSJ k The Wall Street Journal section of the Penn Treebank Project (Marcus et al., 1993) ◮ ... stripped of punctuation, etc. ◮ ... rid of sentences left with more than k POS tags; ◮ ... and converted to reference dependencies — { t ∗ } , using “head percolation rules” (Collins, 1999) . Training: traditionally, WSJ10 (Klein, 2005) ; Spitkovsky et al. (Stanford & Google) Viterbi EM CoNLL (2010-07-15) 8 / 26

  12. The Data WSJ Standard Corpus: WSJ k The Wall Street Journal section of the Penn Treebank Project (Marcus et al., 1993) ◮ ... stripped of punctuation, etc. ◮ ... rid of sentences left with more than k POS tags; ◮ ... and converted to reference dependencies — { t ∗ } , using “head percolation rules” (Collins, 1999) . Training: traditionally, WSJ10 (Klein, 2005) ; Evaluation: Section 23 of WSJ ∞ (all sentences). Spitkovsky et al. (Stanford & Google) Viterbi EM CoNLL (2010-07-15) 8 / 26

  13. The Data WSJ Standard Corpus: WSJ k 45 900 Sentences (1,000s) 40 800 35 700 30 600 25 500 20 400 15 300 10 200 Tokens (1,000s) 5 100 5 10 15 20 25 30 35 40 45 WSJ k Spitkovsky et al. (Stanford & Google) Viterbi EM CoNLL (2010-07-15) 9 / 26

  14. The Data WSJ Standard Corpus: WSJ k 45 900 Sentences (1,000s) 40 800 35 700 30 600 25 500 20 400 15 300 10 200 Tokens (1,000s) 5 100 5 10 15 20 25 30 35 40 45 WSJ k Spitkovsky et al. (Stanford & Google) Viterbi EM CoNLL (2010-07-15) 9 / 26

  15. Results Classic EM Classic EM: The Lay of the Land Directed Dependency Accuracy (%) on WSJ40 70 60 50 40 30 20 10 5 10 15 20 25 30 35 40 WSJ k

  16. Results Classic EM Classic EM: The Lay of the Land Directed Dependency Accuracy (%) on WSJ40 70 60 50 40 30 20 Uninformed 10 5 10 15 20 25 30 35 40 WSJ k

  17. Results Classic EM Classic EM: The Lay of the Land Directed Dependency Accuracy (%) on WSJ40 70 60 50 40 30 20 Uninformed 10 5 10 15 20 25 30 35 40 WSJ k

  18. Results Classic EM Classic EM: The Lay of the Land Directed Dependency Accuracy (%) on WSJ40 70 Oracle 60 50 40 30 20 Uninformed 10 5 10 15 20 25 30 35 40 WSJ k

  19. Results Classic EM Classic EM: The Lay of the Land Directed Dependency Accuracy (%) on WSJ40 70 60 50 Oracle 40 30 20 Uninformed 10 5 10 15 20 25 30 35 40 WSJ k

  20. Results Classic EM Classic EM: The Lay of the Land Directed Dependency Accuracy (%) on WSJ40 70 60 50 Oracle 40 30 20 Uninformed K&M ∗ 10 5 10 15 20 25 30 35 40 WSJ k

  21. Results Classic EM Classic EM: The Lay of the Land Directed Dependency Accuracy (%) on WSJ40 70 60 50 Oracle 40 30 20 Uninformed K&M ∗ 10 5 10 15 20 25 30 35 40 WSJ k Spitkovsky et al. (Stanford & Google) Viterbi EM CoNLL (2010-07-15) 10 / 26

  22. Results Viterbi EM Viterbi EM: Results! Directed Dependency Accuracy (%) on WSJ40 70 Oracle 60 50 40 30 20 10 5 10 15 20 25 30 35 40 WSJ k

  23. Results Viterbi EM Viterbi EM: Results! Directed Dependency Accuracy (%) on WSJ40 70 Oracle 60 50 40 30 20 Uninformed 10 5 10 15 20 25 30 35 40 WSJ k

  24. Results Viterbi EM Viterbi EM: Results! Directed Dependency Accuracy (%) on WSJ40 70 Oracle 60 50 40 30 20 Uninformed K&M ∗ 10 5 10 15 20 25 30 35 40 WSJ k Spitkovsky et al. (Stanford & Google) Viterbi EM CoNLL (2010-07-15) 11 / 26

  25. Results Viterbi EM State-of-the-Art Spitkovsky et al. (Stanford & Google) Viterbi EM CoNLL (2010-07-15) 12 / 26

  26. Results Viterbi EM State-of-the-Art Section 23 of WSJ ∞ Right-Branching Baseline 32% (Klein and Manning, 2004) Spitkovsky et al. (Stanford & Google) Viterbi EM CoNLL (2010-07-15) 12 / 26

  27. Results Viterbi EM State-of-the-Art Section 23 of WSJ ∞ Right-Branching Baseline 32% (Klein and Manning, 2004) DMV with Classic EM 34% (Klein and Manning, 2004) 45% (Spitkovsky et al., 2010) Spitkovsky et al. (Stanford & Google) Viterbi EM CoNLL (2010-07-15) 12 / 26

  28. Results Viterbi EM State-of-the-Art Section 23 of WSJ ∞ Right-Branching Baseline 32% (Klein and Manning, 2004) DMV with Classic EM 34% (Klein and Manning, 2004) 45% (Spitkovsky et al., 2010) DMV with Viterbi EM with Smoothing 45% Spitkovsky et al. (Stanford & Google) Viterbi EM CoNLL (2010-07-15) 12 / 26

  29. Results Viterbi EM State-of-the-Art Section 23 of WSJ ∞ Right-Branching Baseline 32% (Klein and Manning, 2004) DMV with Classic EM 34% (Klein and Manning, 2004) 45% (Spitkovsky et al., 2010) DMV with Viterbi EM with Smoothing 45% + Clever Initialization 48% Spitkovsky et al. (Stanford & Google) Viterbi EM CoNLL (2010-07-15) 12 / 26

  30. Results Viterbi EM State-of-the-Art Section 23 of WSJ ∞ Brown100 Right-Branching Baseline 32% (Klein and Manning, 2004) DMV with Classic EM 34% (Klein and Manning, 2004) 45% 43% (Spitkovsky et al., 2010) DMV with Viterbi EM with Smoothing 45% 48% + Clever Initialization 48% 51% Spitkovsky et al. (Stanford & Google) Viterbi EM CoNLL (2010-07-15) 12 / 26

  31. Results Viterbi EM State-of-the-Art Section 23 of WSJ ∞ Brown100 Right-Branching Baseline 32% (Klein and Manning, 2004) DMV with Classic EM 34% (Klein and Manning, 2004) 45% 43% (Spitkovsky et al., 2010) DMV with Viterbi EM ( + 5%) with Smoothing 45% 48% + Clever Initialization 48% 51% Spitkovsky et al. (Stanford & Google) Viterbi EM CoNLL (2010-07-15) 12 / 26

  32. Results Viterbi EM State-of-the-Art Section 23 of WSJ ∞ Brown100 Right-Branching Baseline 32% (Klein and Manning, 2004) DMV with Classic EM 34% (Klein and Manning, 2004) 45% 43% (Spitkovsky et al., 2010) DMV with Viterbi EM ( + 5%) with Smoothing 45% 48% ( + 3%) + Clever Initialization 48% 51% Spitkovsky et al. (Stanford & Google) Viterbi EM CoNLL (2010-07-15) 12 / 26

  33. Interpretation Interpretation: Why Does Viterbi EM Work? Spitkovsky et al. (Stanford & Google) Viterbi EM CoNLL (2010-07-15) 13 / 26

  34. Interpretation Interpretation: Why Does Viterbi EM Work? in theory, Viterbi is a quick-and-dirty approximation Spitkovsky et al. (Stanford & Google) Viterbi EM CoNLL (2010-07-15) 13 / 26

  35. Interpretation Interpretation: Why Does Viterbi EM Work? in theory, Viterbi is a quick-and-dirty approximation in theory, Communism works... Spitkovsky et al. (Stanford & Google) Viterbi EM CoNLL (2010-07-15) 13 / 26

  36. Interpretation Interpretation: Why Does Viterbi EM Work? in theory, Viterbi is a quick-and-dirty approximation in theory, Communism works... in practice, EM emulates supervised learning: Spitkovsky et al. (Stanford & Google) Viterbi EM CoNLL (2010-07-15) 13 / 26

  37. Interpretation Interpretation: Why Does Viterbi EM Work? in theory, Viterbi is a quick-and-dirty approximation in theory, Communism works... in practice, EM emulates supervised learning: s → { t } = T ( s ) Spitkovsky et al. (Stanford & Google) Viterbi EM CoNLL (2010-07-15) 13 / 26

  38. Interpretation Interpretation: Why Does Viterbi EM Work? in theory, Viterbi is a quick-and-dirty approximation in theory, Communism works... in practice, EM emulates supervised learning: s → { t } = T ( s ) Classic EM: w t = P θ ( t | s ) Spitkovsky et al. (Stanford & Google) Viterbi EM CoNLL (2010-07-15) 13 / 26

  39. Interpretation Interpretation: Why Does Viterbi EM Work? in theory, Viterbi is a quick-and-dirty approximation in theory, Communism works... in practice, EM emulates supervised learning: s → { t } = T ( s ) Classic EM: w t = P θ ( t | s ) clearly, this is redistribution of wealth mass Spitkovsky et al. (Stanford & Google) Viterbi EM CoNLL (2010-07-15) 13 / 26

  40. Interpretation Interpretation: Why Does Viterbi EM Work? in theory, Viterbi is a quick-and-dirty approximation in theory, Communism works... in practice, EM emulates supervised learning: s → { t } = T ( s ) Classic EM: w t = P θ ( t | s ) clearly, this is redistribution of wealth mass — also, resembles an omniscient central planner Spitkovsky et al. (Stanford & Google) Viterbi EM CoNLL (2010-07-15) 13 / 26

  41. Interpretation Interpretation: Why Does Viterbi EM Work? in theory, Viterbi is a quick-and-dirty approximation in theory, Communism works... in practice, EM emulates supervised learning: s → { t } = T ( s ) Classic EM: w t = P θ ( t | s ) clearly, this is redistribution of wealth mass — also, resembles an omniscient central planner (knows the true value of everything at all times) Spitkovsky et al. (Stanford & Google) Viterbi EM CoNLL (2010-07-15) 13 / 26

  42. Interpretation Interpretation: Why Does Viterbi EM Work? in theory, Viterbi is a quick-and-dirty approximation in theory, Communism works... in practice, EM emulates supervised learning: s → { t } = T ( s ) Classic EM: w t = P θ ( t | s ) clearly, this is redistribution of wealth mass — also, resembles an omniscient central planner (knows the true value of everything at all times) — could work, given a very powerful model θ ... Spitkovsky et al. (Stanford & Google) Viterbi EM CoNLL (2010-07-15) 13 / 26

  43. Interpretation Interpretation: How Does Classic EM Fail? Spitkovsky et al. (Stanford & Google) Viterbi EM CoNLL (2010-07-15) 14 / 26

  44. Interpretation Interpretation: How Does Classic EM Fail? our model is quite weak (e.g., doesn’t handle agreement) Spitkovsky et al. (Stanford & Google) Viterbi EM CoNLL (2010-07-15) 14 / 26

  45. Interpretation Interpretation: How Does Classic EM Fail? our model is quite weak (e.g., doesn’t handle agreement) reserves a lot of mass for ludicrous parse trees... Spitkovsky et al. (Stanford & Google) Viterbi EM CoNLL (2010-07-15) 14 / 26

  46. Interpretation Interpretation: How Does Classic EM Fail? our model is quite weak (e.g., doesn’t handle agreement) reserves a lot of mass for ludicrous parse trees... — each entitled to non-trivial support by the distribution Spitkovsky et al. (Stanford & Google) Viterbi EM CoNLL (2010-07-15) 14 / 26

  47. Interpretation Interpretation: How Does Classic EM Fail? our model is quite weak (e.g., doesn’t handle agreement) reserves a lot of mass for ludicrous parse trees... — each entitled to non-trivial support by the distribution at small scales, this is not a problem (short sentences) Spitkovsky et al. (Stanford & Google) Viterbi EM CoNLL (2010-07-15) 14 / 26

  48. Interpretation Interpretation: How Does Classic EM Fail? our model is quite weak (e.g., doesn’t handle agreement) reserves a lot of mass for ludicrous parse trees... — each entitled to non-trivial support by the distribution at small scales, this is not a problem (short sentences) — only so many possible parses → few free-loaders Spitkovsky et al. (Stanford & Google) Viterbi EM CoNLL (2010-07-15) 14 / 26

  49. Interpretation Interpretation: How Does Classic EM Fail? our model is quite weak (e.g., doesn’t handle agreement) reserves a lot of mass for ludicrous parse trees... — each entitled to non-trivial support by the distribution at small scales, this is not a problem (short sentences) — only so many possible parses → few free-loaders eventually, exponentially many trees (unwashed masses) Spitkovsky et al. (Stanford & Google) Viterbi EM CoNLL (2010-07-15) 14 / 26

  50. Interpretation Interpretation: How Does Classic EM Fail? our model is quite weak (e.g., doesn’t handle agreement) reserves a lot of mass for ludicrous parse trees... — each entitled to non-trivial support by the distribution at small scales, this is not a problem (short sentences) — only so many possible parses → few free-loaders eventually, exponentially many trees (unwashed masses) result: a dog of a probability distribution... Spitkovsky et al. (Stanford & Google) Viterbi EM CoNLL (2010-07-15) 14 / 26

  51. Interpretation Interpretation: How Does Classic EM Fail? our model is quite weak (e.g., doesn’t handle agreement) reserves a lot of mass for ludicrous parse trees... — each entitled to non-trivial support by the distribution at small scales, this is not a problem (short sentences) — only so many possible parses → few free-loaders eventually, exponentially many trees (unwashed masses) result: a dog of a probability distribution... Spitkovsky et al. (Stanford & Google) Viterbi EM CoNLL (2010-07-15) 14 / 26

  52. Interpretation Interpretation: How Does Classic EM Fail? our model is quite weak (e.g., doesn’t handle agreement) reserves a lot of mass for ludicrous parse trees... — each entitled to non-trivial support by the distribution at small scales, this is not a problem (short sentences) — only so many possible parses → few free-loaders eventually, exponentially many trees (unwashed masses) result: a dog of a probability distribution... ... wagged by its very long tail Spitkovsky et al. (Stanford & Google) Viterbi EM CoNLL (2010-07-15) 14 / 26

  53. Interpretation Interpretation: Idealogical Difference! Spitkovsky et al. (Stanford & Google) Viterbi EM CoNLL (2010-07-15) 15 / 26

  54. Interpretation Interpretation: Idealogical Difference! Viterbi EM is powered by greed (much like Capitalism) Spitkovsky et al. (Stanford & Google) Viterbi EM CoNLL (2010-07-15) 15 / 26

  55. Interpretation Interpretation: Idealogical Difference! Viterbi EM is powered by greed (much like Capitalism) does not require ability to properly value all parse trees Spitkovsky et al. (Stanford & Google) Viterbi EM CoNLL (2010-07-15) 15 / 26

  56. Interpretation Interpretation: Idealogical Difference! Viterbi EM is powered by greed (much like Capitalism) does not require ability to properly value all parse trees so long as it can spot a decent one (winner-take-all) Spitkovsky et al. (Stanford & Google) Viterbi EM CoNLL (2010-07-15) 15 / 26

  57. Interpretation Interpretation: Idealogical Difference! Viterbi EM is powered by greed (much like Capitalism) does not require ability to properly value all parse trees so long as it can spot a decent one (winner-take-all) different (weaker?) requirement on models: (like IR) Spitkovsky et al. (Stanford & Google) Viterbi EM CoNLL (2010-07-15) 15 / 26

  58. Interpretation Interpretation: Idealogical Difference! Viterbi EM is powered by greed (much like Capitalism) does not require ability to properly value all parse trees so long as it can spot a decent one (winner-take-all) different (weaker?) requirement on models: (like IR) — θ needs to be just discriminative enough! (ranking) Spitkovsky et al. (Stanford & Google) Viterbi EM CoNLL (2010-07-15) 15 / 26

  59. Interpretation Interpretation: Idealogical Difference! Viterbi EM is powered by greed (much like Capitalism) does not require ability to properly value all parse trees so long as it can spot a decent one (winner-take-all) different (weaker?) requirement on models: (like IR) — θ needs to be just discriminative enough! (ranking) at small scales, data are too sparse (markets are illiquid) Spitkovsky et al. (Stanford & Google) Viterbi EM CoNLL (2010-07-15) 15 / 26

  60. Interpretation Interpretation: Idealogical Difference! Viterbi EM is powered by greed (much like Capitalism) does not require ability to properly value all parse trees so long as it can spot a decent one (winner-take-all) different (weaker?) requirement on models: (like IR) — θ needs to be just discriminative enough! (ranking) at small scales, data are too sparse (markets are illiquid) improves with more data (statistics become efficient) Spitkovsky et al. (Stanford & Google) Viterbi EM CoNLL (2010-07-15) 15 / 26

  61. Interpretation Interpretation: Idealogical Difference! Viterbi EM is powered by greed (much like Capitalism) does not require ability to properly value all parse trees so long as it can spot a decent one (winner-take-all) different (weaker?) requirement on models: (like IR) — θ needs to be just discriminative enough! (ranking) at small scales, data are too sparse (markets are illiquid) improves with more data (statistics become efficient) — really, what we want from unsupervised learners! Spitkovsky et al. (Stanford & Google) Viterbi EM CoNLL (2010-07-15) 15 / 26

  62. Interpretation Interpretation: Summary Spitkovsky et al. (Stanford & Google) Viterbi EM CoNLL (2010-07-15) 16 / 26

  63. Interpretation Interpretation: Summary Viterbi EM: focus on the individual best parse trees Spitkovsky et al. (Stanford & Google) Viterbi EM CoNLL (2010-07-15) 16 / 26

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