HPSG parser development at U- tokyo

HPSG parser developmentat U-tokyo

Takuya Matsuzaki

University of Tokyo

Topics

• Overview of U-Tokyo HPSG parsing system• Supertagging with Enju HPSG grammar

Overview of U-Tokyo parsing system

• Two different algorithms:– Enju parser: Supertagging + CKY algo. for TFS– Mogura parser: Supertagging + CFG-filtering

• Two disambiguation models:– one trained on PTB-WSJ– one trained on PTB-WSJ + Genia (biomedical)

Supertagger-based parsing [Clark and Curran, 2004; Ninomiya et al., 2006]

• Supertagging [Bangalore and Joshi, 1999]:Selecting a few LEs for a word by using a probabilistic model of P(LE | sentence)

I like it

HEAD nounSUBJ < >

COMPS < >HEAD nounSUBJ < >





COMPS < >

HEAD verbSUBJ <NP>

COMPS <NP>HEAD verb

SUBJ <NP>COMPS <NP>

HEAD verbSUBJ <NP>

COMPS <NP>HEAD verb

SUBJ <NP>COMPS <NP>

HEAD verbSUBJ <NP>

COMPS <NP>HEAD verb

SUBJ <NP>COMPS <NP>

HEAD nounSUBJ < >






COMPS < >P: large

P: small

• Ignore the LEs with small probabilities

I like it

HEAD nounSUBJ < >






COMPS < >

HEAD verbSUBJ <NP>

COMPS <NP>HEAD verb

SUBJ <NP>COMPS <NP>

HEAD verbSUBJ <NP>

COMPS <NP>HEAD verb

SUBJ <NP>COMPS <NP>

HEAD verbSUBJ <NP>

COMPS <NP>HEAD verb

SUBJ <NP>COMPS <NP>

HEAD nounSUBJ < >






COMPS < >P: large

P: small

Supertagger-based parsing [Clark and Curran, 2004; Ninomiya et al., 2006]

Input to the parser

LEs with P > threshold

I like it

HEAD nounSUBJ < >



COMPS < >

HEAD verbSUBJ <NP>

COMPS <NP>HEAD verb

SUBJ <NP>COMPS <NP>

HEAD nounSUBJ < >


COMPS < >

threshold

Flow in Enju parser

1. POS tagging by a CRF-based model2. Morphological analysis (inflected base

form) by the WordNet dictionary3. Multi-Supertagging by a MaxEnt model4. TFS CKY parsing + MaxEnt disambiguation on

the multi-supertagged sentence

Flow in Mogura parser

1. POS tagging by a CRF-based model2. Morphological analysis (inflected base

form) by the WordNet dictionary3. Supertagging by a MaxEnt model4. Selection of (probably) constraint-satisfying

supertag assignment5. TFS shift-reduce parsing on singly-

supertagged sentence

• Ignore the LEs with small probabilities

I like it

HEAD nounSUBJ < >






COMPS < >

HEAD verbSUBJ <NP>

COMPS <NP>HEAD verb

SUBJ <NP>COMPS <NP>

HEAD verbSUBJ <NP>

COMPS <NP>HEAD verb

SUBJ <NP>COMPS <NP>

HEAD verbSUBJ <NP>

COMPS <NP>HEAD verb

SUBJ <NP>COMPS <NP>

HEAD nounSUBJ < >






COMPS < >P: large

P: small

Previous supertagger-based parsing [Clark and Curran, 2004; Ninomiya et al., 2006]

Input to the parser

LEs with P > threshold

I like it

HEAD nounSUBJ < >



COMPS < >

HEAD verbSUBJ <NP>

COMPS <NP>HEAD verb

SUBJ <NP>COMPS <NP>

HEAD nounSUBJ < >


COMPS < >

threshold

HEAD nounSUBJ < >

COMPS < >

HEAD verbSUBJ <NP>COMPS <>

HEAD nounSUBJ < >

COMPS < >

HEAD verbSUBJ <>

COMPS <>

like

HEAD verbSUBJ <NP>

COMPS <NP>

Supertagging is “almost parsing”

A dilemma in the previous method• Fewer LEs Faster parsing, but• Too few LEs More risk of no well-formed

parse trees

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HEAD nounSUBJ < >

COMPS < >

HEAD verbSUBJ <NP>

COMPS <VP>

HEAD nounSUBJ < >

COMPS < >

Mogura Overview

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HEAD nounSUBJ < >






COMPS < >

HEAD verbSUBJ <NP>

COMPS <NP>HEAD verb

SUBJ <NP>COMPS <NP>

HEAD verbSUBJ <NP>

COMPS <NP>HEAD verb

SUBJ <NP>COMPS <NP>

HEAD verbSUBJ <NP>

COMPS <NP>HEAD verb

SUBJ <NP>COMPS <NP>

HEAD nounSUBJ < >






COMPS < >

Supertagger

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input sentence

Enumeration of assignments

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HEAD nounSUBJ < >

COMPS < >

HEAD verbSUBJ <NP>

COMPS <NP>

HEAD nounSUBJ < >

COMPS < >

I like it

HEAD nounSUBJ < >

COMPS < >

HEAD verbSUBJ <NP>

COMPS <NP>

HEAD nounSUBJ < >

COMPS < >

I like it

HEAD nounSUBJ < >

COMPS < >

HEAD verbSUBJ <NP>

COMPS <NP>

HEAD nounSUBJ < >

COMPS < >

...

Deterministicdisambiguation

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Prob.

Enumaration of the maybe-parsable LE assignments

( １１１

2 １１

1 2 １

( , , )2 １１

...

I like it

2１ 2１ 2１

... ... ...

Prob.

...

, , )１１１

( , , )2 １１( , , )１ 2 １

Prob.

Supertaggingresult

Enumeration of thehighest-prob. LE sequences

CFG-filter

CFG-filter• Parsing with a CFG that approximates the HPSG [Kiefer

and Krieger, 2000; Torisawa et al, 2000]

– Approximation = elmination of some constraints in the grammar (long-distance dep., number, case, etc.)

– Covering property: if a LE assignment is parsable by the HPSG it is also parsable by the approx. CFG

– CFG parsing is much faster than HPSG parsing

Parser grammar Accuracy Speed

MST parser dependency90.02%

(LAS) 4.5 snt/sec

Sagae’s parser dependency 89.01%(LAS) 21.6 snt/sec

Berkeley parser CFG 89.27%(LF1) 4.7 snt/sec

Charniak’s parser CFG 89.55%(LF1) 2.2 snt/sec

Charniak’s parser reranker　 CFG

91.40 %(LF1) 1.9 snt/sec

Enju parser HPSG 88.87%(PAS-LF1) 2.7 snt/sec

Mogura parser HPSG 88.07%(PAS-LF1) 22.8 snt/sec

Results on PTB-WSJ

Supertagging with Enju grammar• Input: POS-tagged sentence

• Number of supertags (lexical templates): 2,308

• Current implementation– Classifier: MaxEnt, point-wise prediction (i.e., no dependencies among

neighboring supertags)– Features: words and POS tags in -2/+3 window

• 92% token accuracy (1-best, only on covered tokens)

• It’s “almost parsing”: 98-99% parsing accuracy (PAS F1) given correct lexical assignments

Pointwise-Supertagging

P1 P2 P3 P4 P5 P6 P7 P8

w1 w2 w3 w4 w5 w6 w7 w8

S1 S2 S3 S4 S5 S6 S7 S8

Input

Output

Lex. Ent.

POS tag

Word


P1 P2 P3 P4 P5 P6 P7 P8

w1 w2 w3 w4 w5 w6 w7 w8

S1 S2 S3 S4 S5 S6 S7 S8

Input

Output

Lex. Ent.

POS tag

Word


P1 P2 P3 P4 P5 P6 P7 P8

w1 w2 w3 w4 w5 w6 w7 w8

S1 S2 S3 S4 S5 S6 S7 S8

Input

Output

Lex. Ent.

POS tag

Word


P1 P2 P3 P4 P5 P6 P7 P8

w1 w2 w3 w4 w5 w6 w7 w8

S1 S2 S3 S4 S5 S6 S7 S8

Input

Output

Lex. Ent.

POS tag

Word


P1 P2 P3 P4 P5 P6 P7 P8

w1 w2 w3 w4 w5 w6 w7 w8

S1 S2 S3 S4 S5 S6 S7 S8

Input

Output

Lex. Ent.

POS tag

Word


P1 P2 P3 P4 P5 P6 P7 P8

w1 w2 w3 w4 w5 w6 w7 w8

S1 S2 S3 S4 S5 S6 S7 S8

Input

Output

Lex. Ent.

POS tag

Word

Supertagging: future directions• Basic strategy: do more work in supertagging (rather than in

parsing)• Pros

– Model/algorithm is simpler Easy error analysis Various features without extending the parsing algorithm Fast try-and-error cycle for feature engineering

• Cons– No tree structure Feature design is sometimes tricky/ad-hoc:

e.g., “nearest preceding verb/noun”, instead of “possible modifiee of a PP”

Supertagging: future directions

• Recovery from POS-tagging error in supertagging stage

• Incorporation of shallow processing results (e.g., chunking, NER, coordination structure prediction) as new features

• Comparison across other languages/grammar frameworks

Thank you!

Deterministic disambiguation• Implemented as a shift-reduce parser– Deterministic parsing: only one analysis at one time– Next parsing action is selected using a scoring

function

next action ),,(maxarg QSaFaAa

• F: scoring function (averaged-perceptron algorithm [Collins and Duffy, 2002])• Features are extracted from the stack state S and lookahead queue Q• A: the set of possible actions (CFG-forest is used as a `guide’)

Example

I like it

HEAD nounSUBJ < >

COMPS < >

HEAD verbSUBJ <NP>

COMPS <NP>

HEAD nounSUBJ < >

COMPS < >

Initial stateS Q

HEAD nounSUBJ < >

COMPS < >

HEAD verbSUBJ <NP>

COMPS <NP>

HEAD nounSUBJ < >

COMPS < >

argmax F(a, S, Q) = SHIFT

I like it

S Q

HEAD nounSUBJ < >

COMPS < >

HEAD verbSUBJ <NP>

COMPS <NP>

HEAD nounSUBJ < >

COMPS < >

I like it

S Qargmax F(a, S, Q) = SHIFT

HEAD nounSUBJ < >

COMPS < >

HEAD verbSUBJ <NP>

COMPS <NP>

HEAD nounSUBJ < >

COMPS < >

I like it

S Qargmax F(a, S, Q) = SHIFT

HEAD nounSUBJ < >

COMPS < >

argmax F(a, S, Q) = REDUCE(Head_Comp)

I

like it

HEAD verbSUBJ <[1]>

COMPS <NP>

HEAD nounSUBJ < >

COMPS < >

HEAD verbSUBJ <[1]NP>

COMPS <>

Head-Comp-Schema

S Q

argmax F(a, S, Q) = REDUCE(Subj_Head)

I

like it

HEAD verbSUBJ <[1]>

COMPS <NP>

HEAD nounSUBJ < >

COMPS < >

HEAD verbSUBJ <[1]NP>COMPS <>

HEAD nounSUBJ < >

COMPS < >

HEAD verbSUBJ <>

COMPS <>

Subj-Head-Schema

S Q

Documents

HPSG parser development at U- tokyo