1 / 30

LING 438/538 Computational Linguistics

LING 438/538 Computational Linguistics. Sandiway Fong Lecture 26. Administrivia. Reminder 538 requirement Email me chapter/section presentation choices (1st-3rd) Range: chapter 14 through 25: first come, first served…. Today’s Topics. We didn’t finish reviewing Homework 6 …

magar
Download Presentation

LING 438/538 Computational Linguistics

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. LING 438/538Computational Linguistics Sandiway Fong Lecture 26

  2. Administrivia • Reminder • 538 requirement • Email me chapter/section presentation choices (1st-3rd) • Range: chapter 14 through 25: first come, first served…

  3. Today’s Topics • We didn’t finish reviewing Homework 6 … • Finite State Transducers (FST) • Background: JM sections 3.4-3.7 • English spelling rules • Homework 7 (due next Thursday)

  4. Homework 6 Review Examples: • (a) Johnpraises himself • (a) John thinks he is smart • (a) Johnconsiders himselfto be intelligent • (a) John likes his dog • (a) John found a picture of himself • (a) John found Mary’s picture of herself Examples: • (b) Marypraises herself • (b) Mary thinks she is smart • (b) Maryconsiders herselfto be intelligent • (b) Mary likes her dog • (b) Mary found a picture of herself • (b) Mary found John’s picture of himself Question 1: write a Prolog grammar for the following sentences

  5. Homework 6 Review • It’s straightforward to build a grammar to cover the examples • unfortunately, it also overgenerates … • We want to rule out ungrammatical examples: • *Johnpraises herself • *John thinks himself is smart • *Johnconsiders herselfto be intelligent • *John likes himself’s dog • *John found a picture of herself • *John found Mary’s picture of himself

  6. Homework 6 Review Idea: propagate value of lexical feature Gender up the tree

  7. Homework 6 Review

  8. Homework 6 Review

  9. Homework 6 Review m f m m m f m m m f

  10. Homework 6 Review m m m f m f m m m f m f

  11. Homework 6 Review m f m m m m f m f m f m f m

  12. Homework 6 Review G m G m f f m f f f m f f f f m

  13. Homework 6 Review

  14. Homework 6 Review she Can’t use unrestricted Gender feature percolation, otherwise *she

  15. Homework 6 Review Practical solution: block anaphor from appearing in subject position under sbar. she Key linguistic insight: anaphors and pronouns behave differently!

  16. Homework 6 Review • Practical solution: • prevent anaphor from appearing in subject position under sbar. • (allow pronoun) Two categories of person pronouns: prp and prp1 np1 behaves just like np but cannot access prp1

  17. Homework 6 Review • Practical solution: • prevent anaphor from appearing in subject position under sbar. • (allow pronoun) np1 behaves just like np but cannot access prp1

  18. Homework 6 Review • Practical solution: • prevent anaphor from appearing in subject position under sbar. • (allow pronoun)

  19. Homework 6 Review • For information on a more general solution … • Google Binding Theory

  20. Homework 6 Review Feature percolation implementation is difficult… maybe impossible… Local usually means in the same S c-command (constituent command)

  21. Today’s Topic • Going to step away from sentence level syntax, and go back to talking about words (for a couple of lectures) … • Let’s talk about a generalization of the finite state automaton (FSA); the finite state transducer (FST)

  22. Finite State Transducers (FST) • Problem: • not all FSTs can be turned into deterministic FST (DFST) • i.e. non-deterministic FST and DFST are not equivalent in power • e.g. DFST can only compute functions, no way to handle one-to-many relations: a:b > 1 2 There are also functions than non-deterministic FST can compute but not DFST a:c 3 • Restrictions (so that things can be determinized): • Sequential transducers: • deterministic on the input side • No epilson (ε) on input side – ok on output side • Subsequential transducers = sequential transducer + extra tail output at final state(s)

  23. Spelling Rules • aka orthographic rules • Examples: Note: the Porter stemmer tries to reconstruct these… • Idea: apply orthographic rules to fix up the output a morphological parsing FST:

  24. Spelling Rules • Tlex:

  25. e-insertion FST • Context-sensitive rule: rewrite right context left context • Corresponding FST: other = any feasible pair not in this transducer

  26. e-insertion FST other = any feasible pair not in this transducer i.e. anything not covered by the other columns in the table • State transition table: • FST:

  27. e-insertion FST • State transition table: • FST: Input q0 q0 q0 q1 q2 q5 Reject q4 q0 q3 Accept Output

  28. e-insertion FST • State transition table: • FST: Input Accept q0 q0 q1 q1 q0 q0 q0 Output

  29. Spelling Rules • aka orthographic rules • Examples: • Idea: apply orthographic rules to fix up the output a morphological parsing FST:

  30. Homework 7 • Input: verb_stem^morpheme# ^ = morpheme boundary # = word boundary • try^s# ⤇ tries • try^ed# ⤇ tried • play^s# ⤇ plays • play^ed# ⤇ played • yank^s# ⤇ yank^s# • yank^ed# ⤇ yank^ed# Draw a FST that handles Y replacement for the examples shown Give the state transition table Implement your table in Perl Show working examples

More Related