a cyk variant for scfg decoding without a dot chart
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A CYK+ Variant for SCFG Decoding Without a Dot Chart Rico Sennrich - PowerPoint PPT Presentation

A CYK+ Variant for SCFG Decoding Without a Dot Chart Rico Sennrich Institute for Language, Cognition and Computation University of Edinburgh October 25 2014 R. Sennrich Recursive CYK+ 1 / 15 Outline CYK+ and the role of the dot chart


  1. A CYK+ Variant for SCFG Decoding Without a Dot Chart Rico Sennrich Institute for Language, Cognition and Computation University of Edinburgh October 25 2014 R. Sennrich Recursive CYK+ 1 / 15

  2. Outline CYK+ and the role of the dot chart Recursive variant Evaluation R. Sennrich Recursive CYK+ 2 / 15

  3. Problem CYK+ parsing CYK+ and Earley-style variants are popular parsers for decoding with SCFGs (Moses, cdec, SAMT, Jane, ...). alternative: binarization and decoding with plain CYK. problem CYK+ parsing [with syntactic models] takes a lot of memory. n = 20 n = 40 n = 80 0.32 GB 2.63 GB 51.64 GB most of the memory is consumed by the dot chart. R. Sennrich Recursive CYK+ 3 / 15

  4. Problem CYK+ parsing CYK+ and Earley-style variants are popular parsers for decoding with SCFGs (Moses, cdec, SAMT, Jane, ...). alternative: binarization and decoding with plain CYK. problem CYK+ parsing [with syntactic models] takes a lot of memory. n = 20 n = 40 n = 80 0.32 GB 2.63 GB 51.64 GB most of the memory is consumed by the dot chart. solution in this talk, we present a variant of CYK+ without a dot chart. our variant requires less memory and is faster, with same result. R. Sennrich Recursive CYK+ 3 / 15

  5. CYK+ The CYK+ algorithm bottom-up chart parser generalization of CYK to n -ary rules two data structures: main chart: non-terminal symbols dot chart: rule prefix applications (dotted items) difference to Earley: dotted item represents all rules with same prefix dot chart allows dynamic binarization: rules that match span (i,j) are found by combining dotted item in (i,k) and (non-)terminal symbol in span (k,j). R. Sennrich Recursive CYK+ 4 / 15

  6. CYK+ it is a trap it is a trap 1 1 → S NP V NP 2 2 NP → ART NN 3 3 4 4 → NP it 5 5 V → is 6 6 → ART a 7 7 8 8 NN → trap 9 9 10 10 dot chart main chart grammar CYK+ steps search for terminal rule of size 1. 1 combine dotted item and (non-)terminal of two subspans. 2 create new dotted item from (non-)terminal in cell. 3 R. Sennrich Recursive CYK+ 5 / 15

  7. CYK+ it is a trap it is a trap 1 1 NP → S NP V NP 2 2 NP → ART NN 3 3 4 4 → NP it 5 5 V → is 6 6 → ART a 7 7 8 8 NN → trap 9 9 10 10 dot chart main chart grammar CYK+ steps search for terminal rule of size 1. 1 combine dotted item and (non-)terminal of two subspans. 2 create new dotted item from (non-)terminal in cell. 3 R. Sennrich Recursive CYK+ 5 / 15

  8. CYK+ it is a trap it is a trap 1 NP • 1 NP → S NP V NP 2 2 NP → ART NN 3 3 4 4 → NP it 5 5 V → is 6 6 → ART a 7 7 8 8 NN → trap 9 9 10 10 dot chart main chart grammar CYK+ steps search for terminal rule of size 1. 1 combine dotted item and (non-)terminal of two subspans. 2 create new dotted item from (non-)terminal in cell. 3 R. Sennrich Recursive CYK+ 5 / 15

  9. CYK+ it is a trap it is a trap 1 NP • 1 NP → S NP V NP 2 2 V NP → ART NN 3 3 4 4 → NP it 5 5 V → is 6 6 → ART a 7 7 8 8 NN → trap 9 9 10 10 dot chart main chart grammar CYK+ steps search for terminal rule of size 1. 1 combine dotted item and (non-)terminal of two subspans. 2 create new dotted item from (non-)terminal in cell. 3 R. Sennrich Recursive CYK+ 5 / 15

  10. CYK+ it is a trap it is a trap 1 NP • 1 NP → S NP V NP 2 2 V NP → ART NN 3 3 ART 4 4 → NP it 5 5 V → is 6 6 → ART a 7 7 8 8 NN → trap 9 9 10 10 dot chart main chart grammar CYK+ steps search for terminal rule of size 1. 1 combine dotted item and (non-)terminal of two subspans. 2 create new dotted item from (non-)terminal in cell. 3 R. Sennrich Recursive CYK+ 5 / 15

  11. CYK+ it is a trap it is a trap 1 NP • 1 NP → S NP V NP 2 2 V NP → ART NN 3 3 ART • ART 4 4 → NP it 5 5 V → is 6 6 → ART a 7 7 8 8 NN → trap 9 9 10 10 dot chart main chart grammar CYK+ steps search for terminal rule of size 1. 1 combine dotted item and (non-)terminal of two subspans. 2 create new dotted item from (non-)terminal in cell. 3 R. Sennrich Recursive CYK+ 5 / 15

  12. CYK+ it is a trap it is a trap 1 NP • 1 NP → S NP V NP 2 2 V NP → ART NN 3 3 ART • ART 4 4 NN → NP it 5 5 V → is 6 6 → ART a 7 7 8 8 NN → trap 9 9 10 10 dot chart main chart grammar CYK+ steps search for terminal rule of size 1. 1 combine dotted item and (non-)terminal of two subspans. 2 create new dotted item from (non-)terminal in cell. 3 R. Sennrich Recursive CYK+ 5 / 15

  13. CYK+ it is a trap it is a trap 1 NP • 1 NP → S NP V NP 2 2 V NP → ART NN 3 3 ART • ART 4 4 NN → NP it 5 NP V • 5 V → is 6 6 → ART a 7 7 8 8 NN → trap 9 9 10 10 dot chart main chart grammar CYK+ steps search for terminal rule of size 1. 1 combine dotted item and (non-)terminal of two subspans. 2 create new dotted item from (non-)terminal in cell. 3 R. Sennrich Recursive CYK+ 5 / 15

  14. CYK+ it is a trap it is a trap 1 NP • 1 NP → S NP V NP 2 2 V NP → ART NN 3 3 ART • ART 4 4 NN → NP it 5 NP V • 5 V → is 6 6 → ART a 7 7 NP 8 8 NN → trap 9 9 10 10 dot chart main chart grammar CYK+ steps search for terminal rule of size 1. 1 combine dotted item and (non-)terminal of two subspans. 2 create new dotted item from (non-)terminal in cell. 3 R. Sennrich Recursive CYK+ 5 / 15

  15. CYK+ it is a trap it is a trap 1 NP • 1 NP → S NP V NP 2 2 V NP → ART NN 3 3 ART • ART 4 4 NN → NP it 5 NP V • 5 V → is 6 6 → ART a 7 7 NP 8 8 NN → trap 9 9 10 10 S dot chart main chart grammar CYK+ steps search for terminal rule of size 1. 1 combine dotted item and (non-)terminal of two subspans. 2 create new dotted item from (non-)terminal in cell. 3 R. Sennrich Recursive CYK+ 5 / 15

  16. CYK+: complexity considerations monolingual 1-best parser main chart: O ( n 2 ) dot chart: O ( n 2 ) parsing steps: O ( n 3 ) SCFG decoding Non-locality of LM scores restricts recombination of dotted items [Hopkins and Langmead, 2010] main chart: O ( n 2 ) (with beam search) on the fast jet ski of mr smith the JJ NPB of NNP dot chart: O ( n scope ( G ) ) the JJ NPB of NNP the JJ NPB of NNP parsing steps: O ( n scope ( G ) ) the JJ NPB of NNP choice point choice point rule scope: number of choice points in rule R. Sennrich Recursive CYK+ 6 / 15

  17. The dot chart in SCFG decoding purpose of dot chart allows recombination of different dotted items → does not apply to SCFG decoding allows re-use of same dotted item for different spans it is a trap it is a trap 1 NP • 1 NP 2 2 V 3 3 ART • ART 4 4 NN 5 NP V • 5 6 6 7 7 NP 8 8 9 9 10 10 S dot chart main chart R. Sennrich Recursive CYK+ 7 / 15

  18. The dot chart in SCFG decoding purpose of dot chart allows recombination of different dotted items → does not apply to SCFG decoding allows re-use of same dotted item for different spans it is a trap it is a trap 1 NP • 1 NP 2 2 V 3 3 ART • ART 4 4 NN 5 NP V • 5 6 6 7 7 NP 8 8 9 9 10 10 S dot chart main chart R. Sennrich Recursive CYK+ 7 / 15

  19. The dot chart in SCFG decoding purpose of dot chart allows recombination of different dotted items → does not apply to SCFG decoding allows re-use of same dotted item for different spans it is a trap it is a trap 1 NP • 1 NP 2 2 V 3 3 ART • ART 4 4 NN 5 NP V • 5 6 6 7 7 NP 8 8 9 9 10 10 S dot chart main chart R. Sennrich Recursive CYK+ 7 / 15

  20. The dot chart in SCFG decoding purpose of dot chart allows recombination of different dotted items → does not apply to SCFG decoding allows re-use of same dotted item for different spans it is a trap it is a trap 1 NP • 1 NP 2 2 V 3 3 ART • ART 4 4 NN 5 NP V • 5 6 6 7 7 NP 8 8 9 9 10 10 S dot chart main chart R. Sennrich Recursive CYK+ 7 / 15

  21. A recursive variant Core idea we do not initially know if rule prefix application can be extended. → dotted items are re-visited throughout time. we can change chart traversal order to guarantee that when span (i,k) is visited, all spans (k,j) have been visited before. this eliminates need to store dotted items; instead, they are extended recursively, then discarded. it is a trap it is a trap 1 1 2 2 3 3 4 4 5 5 6 6 7 7 8 8 9 9 10 10 traditional proposed R. Sennrich Recursive CYK+ 8 / 15

  22. Recursive CYK+ it is a trap it is a trap 1 1 → S NP V NP 2 2 NP → ART NN 3 3 4 4 → NP it 5 5 V → is 6 6 → ART a 7 7 8 8 NN → trap 9 9 10 10 dot chart main chart grammar recursive CYK+ steps search for terminal rule of size 1. 1 initial call to rule consume function. 2 recursive call to rule consume function. 3 R. Sennrich Recursive CYK+ 9 / 15

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