THE CYK PARSING METHOD (2)
-
Upload
tashya-hudson -
Category
Documents
-
view
54 -
download
0
description
Transcript of THE CYK PARSING METHOD (2)
![Page 1: THE CYK PARSING METHOD (2)](https://reader035.fdocuments.net/reader035/viewer/2022062304/56812dcf550346895d930f09/html5/thumbnails/1.jpg)
THE CYK PARSING METHOD (2)
Cornelia Kempa
Carla Parra Escartín
WS 2006-2007
![Page 2: THE CYK PARSING METHOD (2)](https://reader035.fdocuments.net/reader035/viewer/2022062304/56812dcf550346895d930f09/html5/thumbnails/2.jpg)
Tübingen, 4th December 2006 2
AGENDA
1. Building the recognition table2. Undoing the effect of the CNF transformation
2.1. Overview2.2. Adding removed elements2.3. Parsing
2.3.1. Methodology2.3.2. Left-most derivation
3. A short retrospective of CYK4. Chart Parsing
![Page 3: THE CYK PARSING METHOD (2)](https://reader035.fdocuments.net/reader035/viewer/2022062304/56812dcf550346895d930f09/html5/thumbnails/3.jpg)
Tübingen, 4th December 2006 3
AGENDA
1. Building the recognition table2. Undoing the effect of the CNF transformation
2.1. Overview2.2. Adding removed elements2.3. Parsing
2.3.1. Methodology2.3.2. Left-most derivation
3. A short retrospective of CYK4. Chart Parsing
![Page 4: THE CYK PARSING METHOD (2)](https://reader035.fdocuments.net/reader035/viewer/2022062304/56812dcf550346895d930f09/html5/thumbnails/4.jpg)
Tübingen, 4th December 2006 4
2. Undoing the effect of the CNF transformation
2.1. Overview (1)
![Page 5: THE CYK PARSING METHOD (2)](https://reader035.fdocuments.net/reader035/viewer/2022062304/56812dcf550346895d930f09/html5/thumbnails/5.jpg)
Tübingen, 4th December 2006 5
2. Undoing the effect of the CNF transformation
2.1. Overview (2)
![Page 6: THE CYK PARSING METHOD (2)](https://reader035.fdocuments.net/reader035/viewer/2022062304/56812dcf550346895d930f09/html5/thumbnails/6.jpg)
Tübingen, 4th December 2006 6
2. Undoing the effect of the CNF transformation
2.1. Overview (3)
![Page 7: THE CYK PARSING METHOD (2)](https://reader035.fdocuments.net/reader035/viewer/2022062304/56812dcf550346895d930f09/html5/thumbnails/7.jpg)
Tübingen, 4th December 2006 7
AGENDA
1. Building the recognition table2. Undoing the effect of the CNF transformation
2.1. Overview
2.2. Adding removed elements2.3. Parsing
2.3.1. Methodology2.3.2. Left-most derivation
3. A short retrospective of CYK4. Chart Parsing
![Page 8: THE CYK PARSING METHOD (2)](https://reader035.fdocuments.net/reader035/viewer/2022062304/56812dcf550346895d930f09/html5/thumbnails/8.jpg)
Tübingen, 4th December 2006 8
2.2. Adding removed elements (1)
2. Undoing the effect of the CNF transformation
![Page 9: THE CYK PARSING METHOD (2)](https://reader035.fdocuments.net/reader035/viewer/2022062304/56812dcf550346895d930f09/html5/thumbnails/9.jpg)
Tübingen, 4th December 2006 9
CYK does not require all non-terminals reachable.
Rule added!!!
+
2.2. Adding removed elements (2)
2. Undoing the effect of the CNF transformation
![Page 10: THE CYK PARSING METHOD (2)](https://reader035.fdocuments.net/reader035/viewer/2022062304/56812dcf550346895d930f09/html5/thumbnails/10.jpg)
Tübingen, 4th December 2006 10
New line
2. Undoing the effect of the CNF transformation
2.2. Adding removed elements (3)
![Page 11: THE CYK PARSING METHOD (2)](https://reader035.fdocuments.net/reader035/viewer/2022062304/56812dcf550346895d930f09/html5/thumbnails/11.jpg)
Tübingen, 4th December 2006 11
Set Rsi, 0
non-terminals that can be considered as possibly occurring just in front of symbol zi
Set Rsn +1,0
non-terminals that can occur at the end of the sentence.
2.2. Adding removed elements (4)
2. Undoing the effect of the CNF transformation
![Page 12: THE CYK PARSING METHOD (2)](https://reader035.fdocuments.net/reader035/viewer/2022062304/56812dcf550346895d930f09/html5/thumbnails/12.jpg)
Tübingen, 4th December 2006 12
AGENDA
1. Building the recognition table2. Undoing the effect of the CNF transformation
2.1. Overview2.2. Adding removed elements
2.3. Parsing2.3.1. Methodology2.3.2. Left-most derivation
3. A short retrospective of CYK4. Chart Parsing
![Page 13: THE CYK PARSING METHOD (2)](https://reader035.fdocuments.net/reader035/viewer/2022062304/56812dcf550346895d930f09/html5/thumbnails/13.jpg)
Tübingen, 4th December 2006 13
Derivation starts with start-symbol S.Is A1A2···Am a right hand side of S?
Does A1A2···Am derive S1,n?
We check this starting with A1
2 cases:
2. Undoing the effect of the CNF transformation2.3. Parsing
2.3.1. Methodology (1)
![Page 14: THE CYK PARSING METHOD (2)](https://reader035.fdocuments.net/reader035/viewer/2022062304/56812dcf550346895d930f09/html5/thumbnails/14.jpg)
Tübingen, 4th December 2006 14
A) A1 is a terminal symbol
it must be the first symbol of s1,n
then check if A2···Am derives s2,n-1
B) A1 is a non-terminal symbol
it must be a member of Rs1,k
then check if A2···Am derives s2,k+1,n-k
2. Undoing the effect of the CNF transformation2.3. Parsing
2.3.1. Methodology (2)
![Page 15: THE CYK PARSING METHOD (2)](https://reader035.fdocuments.net/reader035/viewer/2022062304/56812dcf550346895d930f09/html5/thumbnails/15.jpg)
Tübingen, 4th December 2006 15
Now: determined whether the rule is applicable
if so, which parts of the rule derive which substrings.
Next step: determine how the substrings can be derived.
2. Undoing the effect of the CNF transformation2.3. Parsing
2.3.1. Methodology (3)
![Page 16: THE CYK PARSING METHOD (2)](https://reader035.fdocuments.net/reader035/viewer/2022062304/56812dcf550346895d930f09/html5/thumbnails/16.jpg)
Tübingen, 4th December 2006 16
AGENDA
1. Building the recognition table2. Undoing the effect of the CNF transformation
2.1. Overview2.2. Adding removed elements2.3. Parsing
2.3.1. Methodology
2.3.2. Left-most derivation
3. A short retrospective of CYK4. Chart Parsing
![Page 17: THE CYK PARSING METHOD (2)](https://reader035.fdocuments.net/reader035/viewer/2022062304/56812dcf550346895d930f09/html5/thumbnails/17.jpg)
Tübingen, 4th December 2006 17
2. Undoing the effect of the CNF transformation2.3. Parsing
2.3.2. Left-most derivation (1)
![Page 18: THE CYK PARSING METHOD (2)](https://reader035.fdocuments.net/reader035/viewer/2022062304/56812dcf550346895d930f09/html5/thumbnails/18.jpg)
Tübingen, 4th December 2006 18
2. Undoing the effect of the CNF transformation2.3. Parsing
2.3.2. Left-most derivation (2)
![Page 19: THE CYK PARSING METHOD (2)](https://reader035.fdocuments.net/reader035/viewer/2022062304/56812dcf550346895d930f09/html5/thumbnails/19.jpg)
Tübingen, 4th December 2006 19
This is what we saw so far:
If we continue... The derivation is:
2. Undoing the effect of the CNF transformation2.3. Parsing
2.3.2. Left-most derivation (3)
![Page 20: THE CYK PARSING METHOD (2)](https://reader035.fdocuments.net/reader035/viewer/2022062304/56812dcf550346895d930f09/html5/thumbnails/20.jpg)
Tübingen, 4th December 2006 20
2. Undoing the effect of the CNF transformation2.3. Parsing
2.3.2. Left-most derivation (4)
![Page 21: THE CYK PARSING METHOD (2)](https://reader035.fdocuments.net/reader035/viewer/2022062304/56812dcf550346895d930f09/html5/thumbnails/21.jpg)
Tübingen, 4th December 2006 21
AGENDA
1. Building the recognition table2. Undoing the effect of the CNF transformation
2.1. Overview2.2. Adding removed elements2.3. Parsing
2.3.1. Methodology2.3.2. Left-most derivation
3. A short retrospective of CYK4. Chart Parsing
![Page 22: THE CYK PARSING METHOD (2)](https://reader035.fdocuments.net/reader035/viewer/2022062304/56812dcf550346895d930f09/html5/thumbnails/22.jpg)
Tübingen, 4th December 2006 22
First: recognition table using the original grammar.
Then: transforming grammar to CNF.
3. A short retrospective of CYK (1)
![Page 23: THE CYK PARSING METHOD (2)](https://reader035.fdocuments.net/reader035/viewer/2022062304/56812dcf550346895d930f09/html5/thumbnails/23.jpg)
Tübingen, 4th December 2006 23
For efficiency, CNF is a bit too restrictive
Disadvantage of CNF: • Resulting recognition table lacks the
information we need to construct a derivation using the original grammar!
3. A short retrospective of CYK (2)
![Page 24: THE CYK PARSING METHOD (2)](https://reader035.fdocuments.net/reader035/viewer/2022062304/56812dcf550346895d930f09/html5/thumbnails/24.jpg)
Tübingen, 4th December 2006 24
In the transformation process, some non-terminals were thrown away
(non-productive)Missing information could be added.
3. A short retrospective of CYK (3)
![Page 25: THE CYK PARSING METHOD (2)](https://reader035.fdocuments.net/reader035/viewer/2022062304/56812dcf550346895d930f09/html5/thumbnails/25.jpg)
Tübingen, 4th December 2006 25
Result: almost the same recognition table.• Extra information on non-terminals
• Obtained in a simpler and much more efficient way.
3. A short retrospective of CYK (2)
![Page 26: THE CYK PARSING METHOD (2)](https://reader035.fdocuments.net/reader035/viewer/2022062304/56812dcf550346895d930f09/html5/thumbnails/26.jpg)
Tübingen, 4th December 2006 26
AGENDA
1. Building the recognition table2. Undoing the effect of the CNF transformation
2.1. Overview2.2. Adding removed elements2.3. Parsing
2.3.1. Methodology2.3.2. Left-most derivation
3. A short retrospective of CYK
4. Chart Parsing
![Page 27: THE CYK PARSING METHOD (2)](https://reader035.fdocuments.net/reader035/viewer/2022062304/56812dcf550346895d930f09/html5/thumbnails/27.jpg)
Tübingen, 4th December 2006 27
CYK algorithm also known as chart parsing.
Both techniques variants
(some of them identical among the techniques)
Difference: implementation.
4. Chart parsing (1)
![Page 28: THE CYK PARSING METHOD (2)](https://reader035.fdocuments.net/reader035/viewer/2022062304/56812dcf550346895d930f09/html5/thumbnails/28.jpg)
Tübingen, 4th December 2006 28
A chart is just a recognition table.
4. Chart parsing (2)
![Page 29: THE CYK PARSING METHOD (2)](https://reader035.fdocuments.net/reader035/viewer/2022062304/56812dcf550346895d930f09/html5/thumbnails/29.jpg)
Tübingen, 4th December 2006 29
FINAL OVERVIEW (1)
1. Building the recognition table
2. Possible Derivations
3. Undoing the effect of the CNF transformation.
4. A short retrospective of CYK
5. Chart Parsing
![Page 30: THE CYK PARSING METHOD (2)](https://reader035.fdocuments.net/reader035/viewer/2022062304/56812dcf550346895d930f09/html5/thumbnails/30.jpg)
Tübingen, 4th December 2006 30
PARSING METHODS
Non-directional methods
Top-down Bottom-up
Unger Parser CYK Parser
FINAL OVERVIEW (2)
![Page 31: THE CYK PARSING METHOD (2)](https://reader035.fdocuments.net/reader035/viewer/2022062304/56812dcf550346895d930f09/html5/thumbnails/31.jpg)
THANK YOU VERY MUCH