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Lexical Translation Models 1 January 24, 2013 Thursday, January - PowerPoint PPT Presentation

Lexical Translation Models 1 January 24, 2013 Thursday, January 24, 13 Lexical Translation How do we translate a word? Look it up in the dictionary Haus : house, home, shell, household Multiple translations Different word senses,


  1. Example 0 1 2 3 4 das Haus ist klein NULL 1 3 4 2 Start with a foreign sentence and a target length. Thursday, January 24, 13

  2. Example 0 1 2 3 4 das Haus ist klein NULL 1 3 4 2 Thursday, January 24, 13

  3. Example 0 1 2 3 4 das Haus ist klein NULL 1 3 4 2 Thursday, January 24, 13

  4. Example 0 1 2 3 4 das Haus ist klein NULL the 1 3 4 2 Thursday, January 24, 13

  5. Example 0 1 2 3 4 das Haus ist klein NULL the 1 3 4 2 Thursday, January 24, 13

  6. Example 0 1 2 3 4 das Haus ist klein NULL the house 1 3 4 2 Thursday, January 24, 13

  7. Example 0 1 2 3 4 das Haus ist klein NULL the house 1 3 4 2 Thursday, January 24, 13

  8. Example 0 1 2 3 4 das Haus ist klein NULL the house is 1 3 4 2 Thursday, January 24, 13

  9. Example 0 1 2 3 4 das Haus ist klein NULL the house is 1 3 4 2 Thursday, January 24, 13

  10. Example 0 1 2 3 4 das Haus ist klein NULL the house is small 1 3 4 2 Thursday, January 24, 13

  11. Example 0 1 2 3 4 das Haus ist klein NULL 1 3 4 2 Thursday, January 24, 13

  12. Example 0 1 2 3 4 das Haus ist klein NULL 1 3 4 2 Thursday, January 24, 13

  13. Example 0 1 2 3 4 das Haus ist klein NULL the 1 3 4 2 Thursday, January 24, 13

  14. Example 0 1 2 3 4 das Haus ist klein NULL the 1 3 4 2 Thursday, January 24, 13

  15. Example 0 1 2 3 4 das Haus ist klein NULL house the 1 3 4 2 Thursday, January 24, 13

  16. Example 0 1 2 3 4 das Haus ist klein NULL house the 1 3 4 2 Thursday, January 24, 13

  17. Example 0 1 2 3 4 das Haus ist klein NULL house the is 1 3 4 2 Thursday, January 24, 13

  18. Example 0 1 2 3 4 das Haus ist klein NULL house the is 1 3 4 2 Thursday, January 24, 13

  19. Example 0 1 2 3 4 das Haus ist klein NULL house the is small 1 3 4 2 Thursday, January 24, 13

  20. Finding the Viterbi Alignment a ⇤ = arg a 2 [0 , 1 ,...,n ] m p ( a | e , f ) max p ( e , a | f ) = arg max a 0 p ( e , a 0 | f ) P a 2 [0 , 1 ,...,n ] m = arg a 2 [0 , 1 ,...,n ] m p ( e , a | f ) max 1 n a ∗ i = arg max 1 + np ( e i | f a i ) a i =0 n = arg max a i =0 p ( e i | f a i ) Thursday, January 24, 13

  21. Finding the Viterbi Alignment 0 1 2 3 4 das Haus ist klein NULL the home is little 1 3 4 2 Thursday, January 24, 13

  22. Finding the Viterbi Alignment 0 1 2 3 4 das Haus ist klein NULL the home is little 1 3 4 2 Thursday, January 24, 13

  23. Finding the Viterbi Alignment 0 1 2 3 4 das Haus ist klein NULL the home is little 1 3 4 2 Thursday, January 24, 13

  24. Finding the Viterbi Alignment 0 1 2 3 4 das Haus ist klein NULL the home is little 1 3 4 2 Thursday, January 24, 13

  25. Finding the Viterbi Alignment 0 1 2 3 4 das Haus ist klein NULL the home is little 1 3 4 2 Thursday, January 24, 13

  26. Finding the Viterbi Alignment 0 1 2 3 4 das Haus ist klein NULL the home is little 1 3 4 2 Thursday, January 24, 13

  27. Finding the Viterbi Alignment 0 1 2 3 4 das Haus ist klein NULL the home is little 1 3 4 2 Thursday, January 24, 13

  28. Finding the Viterbi Alignment 0 1 2 3 4 das Haus ist klein NULL the home is little 1 3 4 2 Thursday, January 24, 13

  29. Finding the Viterbi Alignment 0 1 2 3 4 das Haus ist klein NULL the home is little 1 3 4 2 Thursday, January 24, 13

  30. Finding the Viterbi Alignment 0 1 2 3 4 das Haus ist klein NULL the home is little 1 3 4 2 Thursday, January 24, 13

  31. Finding the Viterbi Alignment 0 1 2 3 4 das Haus ist klein NULL the home is little 1 3 4 2 Thursday, January 24, 13

  32. Finding the Viterbi Alignment 0 1 2 3 4 das Haus ist klein NULL the home is little 1 3 4 2 Thursday, January 24, 13

  33. Finding the Viterbi Alignment 0 1 2 3 4 das Haus ist klein NULL the home is little 1 3 4 2 Thursday, January 24, 13

  34. Finding the Viterbi Alignment 0 1 2 3 4 das Haus ist klein NULL the home is little 1 3 4 2 Thursday, January 24, 13

  35. Finding the Viterbi Alignment 0 1 2 3 4 das Haus ist klein NULL the home is little 1 3 4 2 Thursday, January 24, 13

  36. Finding the Viterbi Alignment 0 1 2 3 4 das Haus ist klein NULL the home is little 1 3 4 2 Thursday, January 24, 13

  37. Finding the Viterbi Alignment 0 1 2 3 4 das Haus ist klein NULL the home is little 1 3 4 2 Thursday, January 24, 13

  38. Finding the Viterbi Alignment 0 1 2 3 4 das Haus ist klein NULL the home is little 1 3 4 2 Thursday, January 24, 13

  39. Finding the Viterbi Alignment 0 1 2 3 4 das Haus ist klein NULL the home is little 1 3 4 2 Thursday, January 24, 13

  40. Finding the Viterbi Alignment 0 1 2 3 4 das Haus ist klein NULL the home is little 1 3 4 2 Thursday, January 24, 13

  41. Finding the Viterbi Alignment 0 1 2 3 4 das Haus ist klein NULL the home is little 1 3 4 2 Thursday, January 24, 13

  42. Finding the Viterbi Alignment 0 1 2 3 4 das Haus ist klein NULL the home is little 1 3 4 2 Thursday, January 24, 13

  43. Finding the Viterbi Alignment 0 1 2 3 4 das Haus ist klein NULL the home is little 1 3 4 2 Thursday, January 24, 13

  44. Finding the Viterbi Alignment 0 1 2 3 4 das Haus ist klein NULL the home is little 1 3 4 2 Thursday, January 24, 13

  45. Finding the Viterbi Alignment 0 1 2 3 4 das Haus ist klein NULL the home is little 1 3 4 2 Thursday, January 24, 13

  46. Finding the Viterbi Alignment 0 1 2 3 4 das Haus ist klein NULL the home is little 1 3 4 2 Thursday, January 24, 13

  47. Finding the Viterbi Alignment 0 1 2 3 4 das Haus ist klein NULL the home is little 1 3 4 2 Thursday, January 24, 13

  48. Finding the Viterbi Alignment 0 1 2 3 4 das Haus ist klein NULL the home is little 1 3 4 2 Thursday, January 24, 13

  49. Learning Lexical Translation Models • How do we learn the parameters p ( e | f ) • “Chicken and egg” problem • If we had the alignments, we could estimate the parameters (MLE) • If we had parameters, we could find the most likely alignments Thursday, January 24, 13

  50. EM Algorithm • pick some random (or uniform) parameters • Repeat until you get bored (~ 5 iterations for lexical translation models) • using your current parameters, compute “expected” alignments for every target word token in the training data (on board) p ( a i | e , f ) • keep track of the expected number of times f translates into e throughout the whole corpus • keep track of the expected number of times that f is used as the source of any translation • use these expected counts as if they were “real” counts in the standard MLE equation Thursday, January 24, 13

  51. EM for Model 1 Thursday, January 24, 13

  52. EM for Model 1 Thursday, January 24, 13

  53. EM for Model 1 Thursday, January 24, 13

  54. EM for Model 1 Thursday, January 24, 13

  55. EM for Model 1 Thursday, January 24, 13

  56. Convergence Thursday, January 24, 13

  57. Evaluation • Since we have a probabilistic model, we can evaluate perplexity . 1 ( e , f ) ∈ D | e | log Q ( e , f ) ∈ D p ( e | f ) − P PPL = 2 Iter ∞ Iter 1 Iter 2 Iter 3 Iter 4 ... -log likelihood - 7.66 7.21 6.84 ... -6 perplexity - 2.42 2.30 2.21 ... 2 Thursday, January 24, 13

  58. Alignment Error Rate Thursday, January 24, 13

  59. Alignment Error Rate Possible links P Thursday, January 24, 13

  60. Alignment Error Rate Possible links P Thursday, January 24, 13

  61. Alignment Error Rate Possible links Sure links S P Thursday, January 24, 13

  62. Alignment Error Rate Possible links Sure links S P Thursday, January 24, 13

  63. Alignment Error Rate Possible links Sure links S P Precision( A, P ) = | P ∩ A | | A | Thursday, January 24, 13

  64. Alignment Error Rate Possible links Sure links S P Precision( A, P ) = | P ∩ A | Recall( A, S ) = | S ∩ A | | A | | S | Thursday, January 24, 13

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