exploring propbanks for english and hindi ashwini vaidya dept of linguistics university of colorado,...
TRANSCRIPT
Exploring PropBanks for English and Hindi
Ashwini VaidyaDept of Linguistics
University of Colorado, Boulder
Why is semantic information important?
• Imagine an automatic question answering system• Who created the first effective polio vaccine?• Two possible choices:– Becton Dickinson created the first disposable syringe
for use with the mass administration of the first effective polio vaccine
– The first effective polio vaccine was created in 1952 by Jonas Salk at the University of Pittsburgh
Question Answering
• Who created the first effective polio vaccine?– Becton Dickinson created the first disposable
syringe for use with the mass administration of the first effective polio vaccine
– The first effective polio vaccine was created in 1952 by Jonas Salk at the University of Pittsburgh
Question Answering
• Who created the first effective polio vaccine?– [Becton Dickinson] created the [first disposable
syringe] for use with the mass administration of the first effective polio vaccine
– [The first effective polio vaccine] was created in 1952 by [Jonas Salk] at the University of Pittsburgh
Question Answering
• Who created the first effective polio vaccine?– [Becton Dickinsonagent] created the [first disposable
syringetheme] for use with the mass administration of the first effective polio vaccine
– [The first effective polio vaccinetheme] was created in 1952 by [Jonas Salkagent] at the University of Pittsburgh
Question Answering
• We need semantic information to prefer the right answer
• The theme of create should be ‘the first effective polio vaccine’
• The theme in the first sentence was ‘the first disposable syringe’
• We can filter out the wrong answer
We need semantic information
• To find out about events and their participants• To capture semantic information across
syntactic variation
Semantic information
• Semantic information about verbs and participants expressed through semantic roles
• Agent, Experiencer, Theme, Result etc.
• However, difficult to have a standard set of thematic roles
Proposition Bank
• Proposition Bank (PropBank) provides a way to carry out general purpose Semantic role labelling
• A PropBank is a large annotated corpus of predicate-argument information
• A set of semantic roles is defined for each verb• A syntactically parsed corpus is then tagged
with verb-specific semantic role information
Outline
• English PropBank• Background• Annotation • Frame files & Tagset
• Hindi PropBank development• Adapting Frame files• Light verbs• Mapping from dependency labels
Proposition Bank
• The first (English) PropBank was created on a 1 million syntactically parsed Wall Street Journal corpus
• PropBank annotation has also been done on different genres e.g. web text, biomedical text
• Arabic, Chinese & Hindi PropBanks have been created
English PropBank
• English PropBank envisioned as the next level of Penn Treebank (Kingsbury & Palmer, 2003)
• Added a layer of predicate-argument information to the Penn Treebank
• Broad in its coverage- covering every instance of a verb and its semantic arguments in the corpus
• Amenable to collecting representative statistics
English PropBank Annotation
• Two steps are involved in annotation– Choose a sense ID for the predicate – Annotate the arguments of that predicate with
semantic roles
• This requires two components: frame files and PropBank tagset
PropBank Frame files
• PropBank defines semantic roles on a verb-by-verb basis
• This is defined in a verb lexicon consisting of frame files
• Each predicate will have a set of roles associated with a distinct usage
• A polysemous predicate can have several rolesets within its frame file
An example
• John rings the bell
ring.01 Make sound of bellArg0 Causer of ringing
Arg1 Thing rung
Arg2 Ring for
An example
• John rings the bell• Tall aspen trees ring the lake
ring.01 Make sound of bellArg0 Causer of ringing
Arg1 Thing rung
Arg2 Ring for
ring.02 To surroundArg1 Surrounding entity
Arg2 Surrounded entity
An example
• [John] rings [the bell] • [Tall aspen trees] ring [the lake]
ring.01 Make sound of bellArg0 Causer of ringing
Arg1 Thing rung
Arg2 Ring forring.02 To surroundArg1 Surrounding entity
Arg2 Surrounded entity
Ring.01
Ring.02
An example
• [JohnARG0] rings [the bellARG1]
• [Tall aspen treesARG1] ring [the lakeARG2]
ring.01 Make sound of bellArg0 Causer of ringing
Arg1 Thing rung
Arg2 Ring forring.02 To surroundArg1 Surrounding entity
Arg2 Surrounded entity
Ring.01
Ring.02
Frame files
• The Penn Treebank had about 3185 unique lemmas (Palmer, Gildea, Kingsbury, 2005)
• Most frequently occurring verb: say• Small number of verbs had several framesets
e.g. go, come, take, make• Most others had only one frameset per file
PropBank annotation pane in Jubilee
English PropBank Tagset
• Numbered arguments Arg0, Arg1, and so on until Arg4
• Modifiers with function tags e.g. ArgM-LOC (location) , ArgM-TMP (time), ArgM-PRP (purpose)
• Modifiers give additional information about when, where or how the event occurred
PropBank tagsetNumbered Argument
Description
Arg0 Agent, causer, experiencer
Arg1 Theme, patient
Arg2 Instrument, benefactive, attribute
Arg3 starting point, benefactive, attribute
Arg4 ending point
• Correspond to the valency requirements of the verb• Or, those that occur with high frequency with that verb
PropBank tagset
• 15 modifier labels for English PropBank• [HeArg0] studied [economic growthArg1] [in IndiaArgM-
LOC]
Modifier Description
ArgM-LOC Location
ArgM-TMP Time
ArgM-GOL Goal
ArgM-MNR Manner
ArgM-CAU Cause
ArgM-ADV Adverbial
PropBank tagset
• Verb specific and more generalized • Arg0 and Arg1 correspond to Dowty’s Proto
Roles• Leverage the commonalities among semantic
roles• Agents, causers, experiencers – Arg0• Undergoers, patients, themes- Arg1
PropBank tagset
• While annotating Arg0 and Arg1:– Unaccusative verbs take Arg1 as their subject
argument• [The windowArg1] broke
– Unergatives will take Arg0• [JohnArg0] sang
• Distinction is also made between internally caused events (blush: Arg0) & externally caused events (redden: Arg1)
PropBank tagset
• How might these map to the more familiar thematic roles?
• Yi, Loper & Palmer (2007) describe such a mapping to VerbNet roles
•More frequent Arg0 and Arg1 (85%) are learnt more easily by automatic systems•Arg2 is less frequent, maps to more than one thematic role•Arg3-5 are even more infrequent
Using PropBank
• As a computational resource– Train semantic role labellers (Pradhan et al, 2005)– Question answering systems (with FrameNet)– Project semantic roles onto a parallel corpus in another
language (Pado & Lapata, 2005)
• For linguists, to study various phenomena related to predicate-argument structure
Outline
• English PropBank• Background• Annotation • Frame files & Tagset
• Hindi PropBank development• Adapting Frame files• Light verbs• Mapping from dependency labels
Developing PropBank for Hindi-Urdu
• Hindi-Urdu PropBank is part of a project to develop a Multi-layered and multi-representational treebank for Hindi-Urdu– Hindi Dependency Treebank– Hindi PropBank– Hindi Phrase Structure Treebank
• Ongoing project at CU-Boulder
Hindi-Urdu PropBank
• Corpus of 400,000 words for Hindi• Smaller corpus of 150,000 words for Urdu• Hindi corpus consists of newswire text from
‘Amar Ujala’• So far..– 220 verb frames– ~100K words annotated
Developing Hindi PropBank
• Making a PropBank resource for a new language– Linguistic differences• Capturing relevant language-specific phenomena
– Annotation practices• Maintain similar annotation practices
– Consistency across PropBanks
Developing Hindi PropBank
• PropBank annotation for English, Chinese & Arabic was done on top of phrase structure trees
• Hindi PropBank is annotated on dependency trees
Dependency tree
• Represent relations that hold between constituents (chunks)
• Karaka labels show the relations between head verb and its dependents
दि� ये� gave
k1 k2
पै�से�money
औरत को woman dat
र�म ने�Raam erg
k4
Hindi PropBank
• There are three components to the annotation• Hindi Frame file creation• Insertion of empty categories• Semantic role labelling
Hindi PropBank
• There are three components to the annotation• Hindi Frame file creation• Insertion of empty categories• Semantic role labelling
• Both frame creation and labelling require new strategies for Hindi
Hindi PropBank
• Hindi frame files were adapted to include– Morphological causatives– Unaccusative verbs– Experiencers
• Additionally, changes had to be made to analyze the large number (nearly 40%) of light verbs
Causatives
• Verbs that are related via morphological derivation are grouped together as individual predicates in the same frame file.
• E.g. Cornerstone’s multi-lemma mode is used for the verbs खा� (KA ‘eat’, खिखाला� (KilA ‘feed’ and खिखालावा� (KilvA ‘cause to feed’)
Causatives
raam neArg0 khaanaArg1 khaayaaRam erg food eat-perf
‘Ram ate the food’
mohan neArg0 raam koArg2 khaanaArg1 khilaayaaMohan erg Ram dat food eat-caus-perf
‘Mohan made Ram eat the food’
sita neArgC mohan seArgA raam koArg2 khaanaArg1 khilvaayaaSita erg Mohan instr Ram acc food eat-ind.caus-caus-perf
‘Sita, through Mohan made Ram eat the food ’
Roleset id: KA.01 to eat
Arg0 eater
Arg1 the thing being eaten
Roleset id: KilA.01 to feed
Arg0 feeder
Arg2 eater
Arg1 the thing being eaten
Roleset id: KilvA.01 to cause to be fedArgC Causer of feeding
ArgA feeder
Arg2 Eater
Arg1 the thing eaten
Unaccusatives
• PropBank needs to distinguish proto agents and proto patients
• Sudha danced – – Unergative, animate agentive arguments- Arg0
• The door opened – Unaccusative, non animate patient arguments- Arg1
• For English, these distinctions were available in VerbNet
• For Hindi, various diagnostic tests are applied to make this distinction
YesNo- Second Stage
Ergative. E.g. naac, dauRa, bEtha?
First stage
Yes.Unaccus-ative. E.g. khulnaa, barasnaa
No-Third stage
Yes.Unacc-usative. Eliminate bEtha
No. Take the majority vote on the tests.
cognate object & ergative case tests
Applicable to verbs undergoing transitivity alternation: eliminate those that take (mostly) animate subjects
For non-alternating verbs and others that remain, the verb will be unaccusative if:• Impersonal passives are not possible• use of ‘huaa’ (past participial relative) is possible• the inanimate subject appears without overt genitive
Unaccusativity diagnostics (5)
Unaccusative verb : महक mahak ‘to smell good’
Arg1 entity that smells good
• impersonal passive test• past participial relative test
Unaccusativity
• This information is then captured in the frame
Experiencers
• Arg0 includes agents, causers, experiencers• In Hindi, the experiencer subjects occur with dikhnaa (to
glimpse), milnaa (to find), suujhnaa (to be struck with) etc.• Typically marked with dative case
– Mujh-ko chaand dikhaa I. Dat moon glimpse.pf
(I glimpsed the moon)
• PropBank labels these as Arg0, with an additional
descriptor field ‘experiencer’– Internally caused events
Complex predicates
• A large number of complex predicates in Hindi – Noun-verb complex predicates• vichaar karna; think do (to think)• dhyaan denaa; attention give (to pay attention)
– Adjectives can also occur• accha lagnaa: good seem (to like)
– the predicating element is not the verb alone, but forms a composite with the noun/adj
Complex predicates
• There are also a number of verb-verb complex predicates
• Combine with the bare form of the verb to convey different meanings• ro paRaa; cry lie- burst out crying• Add some aspectual meaning to the verb
• As these occur with only a certain set of verbs, we find them automatically, based on part of speech tag
Complex predicates
• However, the noun-verb complex predicates are more pervasive
• They occur with a large number of nouns• Frame files for the nominal predicate need to
be created• E.g. in a sample of 90K words, the light verb
kar; ‘do’ occurred 1738 times with 298 different nominals
Complex predicates
• Annotation strategy• Additional resources (frame files)
• Cluster the large number of nominals?
Light verb annotation
• A convention for the annotation of light verbs has been adopted across Hindi, Arabic, Chinese and English PropBanks (Hwang et. al. 2010)
• Annotation is carried out in three passes– Manual identification of light verb– Annotation of arguments based on frame file– Deterministic merging of the light verb and ‘true’ predicate
• In Hindi, this process may be simplified because of the dependency label ‘pof’ that identifies a light verb
र�म ने� पै�से� चो र� को�ए
Raam erg Money theft Do.perf
‘Ram stole the money’
1. Identify the N+V sequences that are complex predicates. 2. Annotate predicating expression with ARG-PRX.
REL: karARG-PRX: corii
3. Annotate the arguments and modifiers of the complex predicate with a nominal predicate frame
4. Automatically merge the nominal with the light verb.REL: corii_kiyeArg0: raamArg1: paese
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Hindi PropBank tagset 24 labels
Label DescriptionARG0 Agent, causer, experiencer
ARG1 Patient, theme, undergoer
ARG2 Beneficiary
ARG3 Instrument
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Annotating Hindi PropBank
Label DescriptionARG0 Agent, causer, experiencer
ARG1 Patient, theme, undergoer
ARG2 Beneficiary
ARG3 Instrument
ARG2-ATRARG2-LOC
attribute ARG2-GOLARG2-SOU
goal
location sourceFunction tags
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Annotating Hindi PropBank
Label DescriptionARG0 Agent, causer, experiencer
ARG1 Patient, theme, undergoer
ARG2 Beneficiary
ARG3 Instrument
ARG2-ATRARG2-LOC
attribute ARG2-GOLARG2-SOU
goal
location source
ARGC causer
ARGA secondary causer
Function tags
Causative
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Annotating Hindi PropBank
Label DescriptionARG0 Agent, causer, experiencer
ARG1 Patient, theme, undergoer
ARG2 Beneficiary
ARG3 Instrument
ARG2-ATRARG2-LOC
attribute ARG2-GOLARG2-SOU
goal
location source
ARGC causer
ARGA secondary causer
ARGM-VLV Verb-verb construction
ARGM-PRX Noun-verb construction
Function tags
Causative
Complex predicate
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Annotating Hindi PropBank
Label Description Label Description
ARGM-ADV adverb ARGM-CAU cause
ARGM-DIR direction ARGM-DIS discourse
ARGM-EXT extent ARGM-LOC location
ARGM-MNR manner ARGM-MNS means
ARGM-MOD modal ARGM-NEG negation
ARGM-PRP purpose ARGM-TMP time
•Other modifier labels
Hindi PropBank annotationAnnotation pane Frameset file display
Annotation practice
• Need to maintain good annotation practices• Current practices- double blind, followed by
adjudication• Inter-annotator agreement measures the
consistency in the annotation task• English PropBank had high inter annotator
agreement K=0.91
Hindi PropBank annotation
• Improve consistency & annotation speed• PropBank annotation on dependency trees
has some advantages• Hindi Treebank uses a large set of dependency
labels that have rich semantic informationदि� ये� gave
Arg0k1
Arg1k2
Arg2k4
पै�से�money
औरत को woman dat
र�म ने�Raam erg
Deriving PropBank labels from dependencies
• We can derive Hindi PropBank labels from Dependency labels
• Mapping will reduce annotation effort, improve speed
• The dependency tagset has labels that are in some ways fairly similar to PropBank– Verb specific labels k1- 5– Verb modifier labels k7p, k7t, rh etc.
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Label comparison
•Using linguistic intuition, we can compare HDT labels with the numbered arguments in HPB
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Label comparison
• Similarly, linguistic intuition gives us the mapping from HDT for HPB modifiers
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Label comparison
• These mappings are included in the PB frame files, for example, the verb ‘A: to come’
• Only for numbered arguments• Basis for the linguistically motivated rules
Roleset Usage Rule
A.01 To come (path) k1 Arg1k2p Arg2-GOL
A.03 to arrive k1 Arg0k2p Arg2-GOLk5 Arg2-SOU
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Automatic mapping of DT to PB
• A rule based, probabilistic system for automatic mapping
• We use two kinds of resources:– Annotated corpus [Treebank+ PropBank]• 32,300 tokens, 2005 predicates
– Frame files with mapping rules
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Argument classification
• We use three kinds of rules to carry out automatic mapping– Deterministic rules• Dependency label mapped directly onto PropBank
– Empirically derived rules• Using corpus statistics associated with dependency &
PropBank labels
– Linguistically motivated rules• Derived from linguistic intuition & captured in frame
files
Example of the rulesFeatures Count PropBank labels
xe.01_active_k1(give)
32 Arg0: 0.93
Arg1: 0.03
Arg2:0.03
xe.01_active_k2 65 Arg1:0.95
Arg2:0.01
Arg0:0.01
xe.01_active_k4 34 Arg2:0.94
Arg0:0.02
•Associate the probability of each label in combination with a particular feature tuple •We use only 3: roleset ID, voice, dependency label•For the verb give, we get the correct mapping to the Hindi labels
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Evaluation
• 32,300 tokens of annotated data• Ten-fold cross validation for evaluation
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ResultsPRECISION RECALL F1 SCORE
Empirically derived rules
90.59 47.92 62.69
Linguistically motivated rules
89.80 55.28 68.44
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ResultsPRECISION RECALL F1 SCORE
Empirically derived rules
90.59 47.92 62.69
Linguistically motivated rules
89.80 55.28 68.44
Numbered Argument AccuracyPRECISION RECALL F-SCORE
Empirically derived rules
93.63 58.76 72.21
Linguistically motivated
rules
91.87 72.36 80.96
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Evaluation
• Linguistically motivated rules improve the recall with a slight drop in the precision
• With the most frequent PropBank labels, empirically derived rules perform well
• More data should improve the performance for modifier arguments
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Evaluation
• Annotation practices also affect the mapping– PB labels are coarse-grained: E.g. ArgM-ADV maps
to four different dependency labels
– PB are fine-grained: E.g. ‘means’ and ‘causes’ are distinguished (ArgM-MNS, ArgM-CAU)but are lumped together under a single label in dependency treebank
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Evaluation
• Our goal is to find a useful set of mappings to use at a pre-annotation stage
• We expect that with more PropBanked data, empirically derived rules will perform better
• Using additional resources such as Hindi WordNet can help to make up for the lack of training data
Summary
• Semantic role labels• English PropBank– Frame files– PropBank tagset
• Development of Hindi PropBank– Linguistic issues– Experiments
Questions?