Unambiguous Unlimited = Unsupervised

1
Unambiguous Unlimited Unsupervised

• Marti Hearst
• School of Information, UC Berkeley
• Invited Talk, University of Toronto
• January 31, 2006

This research supported in part by NSF DBI-0317510
2
Natural Language Processing

• The ultimate goal write programs that read and
  understand stories and conversations.
• This is too hard! Instead we tackle
  sub-problems.
• There have been notable successes lately
• Machine translation is vastly improved
• Decent speech recognition in limited
  circumstances
• Text categorization works with some accuracy

3
Why is text analysis difficult?

• One reason enormous vocabulary size.
• The average English speakers vocabulary is
  around 50,000 words,
• Many of these can be combined with many others,
• And they mean different things when they do!

4
Whats a Robot to Do?

• Decorate the cake with the frosting.
• Decorate the cake with the kids.
• Throw out the cake with the frosting.
• Get the sock from the cat with the gloves.
• Get the glove from the cat with the socks.
• Its in the plastic water bottle.
• Its in the plastic bag dispenser.

5
How to tackle this problem?

• The field was stuck for quite some time.
• CYC hand-enter all semantic concepts and
  relations
• A new approach started around 1990
• How to do it
• Get large text collections
• Compute statistics over the words in those
  collections
• Many different algorithms for doing this.

6
Size Matters

• Recent realization bigger better than smarter!
• Banko and Brill 01 Scaling to Very, Very Large
  Corpora for Natural Language Disambiguation, ACL
  

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Example Problem

• Grammar checker example
• Which word to use?
• ltprincipalgt ltprinciplegt
• Look at which words surround each use
• I am in my third year as the principal of Anamosa
  High School.
• School-principal transfers caused some upset.
• This is a simple formulation of the quantum
  mechanical uncertainty principle.
• Power without principle is barren, but principle
  without power is futile. (Tony Blair)

8
Using Very, Very Large Corpora

• Keep track of which words are the neighbors of
  each spelling in well-edited text, e.g.
• Principal high school
• Principle rule
• At grammar-check time, choose the spelling best
  predicted by the surrounding words.
• Surprising results
• Log-linear improvement even to a billion words!
• Getting more data is better than fine-tuning
  algorithms!

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The Effects of LARGE Datasets

• From Banko Brill 01

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How to Extend this Idea?

• This is an exciting result
• BUT relies on having huge amounts of text that
  has been appropriately annotated!

11
How to Avoid Labeling?

• Web as a baseline (Lapata Keller 04,05)
• Main idea apply web-determined counts to every
  problem imaginable.
• Example for t in ltprincipalgt ltprinciplegt
• Compute f(w1, t, w2)
• The largest count wins

12
Web as a Baseline

• Works very well in some cases
• machine translation candidate selection
• article generation
• noun compound interpretation
• noun compound bracketing
• adjective ordering
• But lacking in others
• spelling correction
• countability detection
• prepositional phrase attachment
• How to push this idea further?

Significantly better than the best supervised
algorithm.
Not significantly different from the best
supervised.
13
Using Unambiguous Cases

• The trick look for unambiguous cases to start
• Use these to improve the results beyond what
  co-occurrence statistics indicate.
• An Early Example
• Hindle and Rooth, Structural Ambiguity and
  Lexical Relations, ACL 90, Comp Ling93
• Problem Prepositional Phrase attachment
• I eat/v spaghetti/n1 with/p a fork/n2.
• I eat/v spaghetti/n1 with/p sauce/n2.
• quadruple (v, n1, p, n2)
• Question does n2 attach to v or to n1?

14
Using Unambiguous Cases

• How to do this with unlabeled data?
• First try
• Parse some text into phrase structure
• Then compute certain co-occurrences
• f(v, n1, p) f(n1, p) f(v, n1)
• Problem results not accurate enough
• The trick look for unambiguous cases
• Spaghetti with sauce is delicious. (pre-verbal)
• I eat it with a fork. (object of preposition
  cant attach to a pronoun)
• Use these to improve the results beyond what
  co-occurrence statistics indicate.

15
Using Unambiguous Cases

• Hindle Rooth, final algorithm
• Parse text into phrase structure.
• Create bigram counts (v, p) and (n1, p) as
  follows
• First, use unambiguous cases to populate bigram
  table
• Then, for the ambiguous cases
• Compute a Lexical Association score comparing
  (v1, n1, p) to (n1, p, n2).
• If this is greater than a threshold, update the
  bigram table with the assumed attachment
• Else split the score and assign to both
  attachments
• The bigram table is used for further computations
  of the Lexical Association score.

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Unambiguous Unlimited Unsupervised

• Apply the Unambiguous Case Idea to the Very, Very
  Large Corpora idea
• The potential of these approaches are not fully
  realized
• Our work
• Semantic Relation Acquisition
• Hypernym (ISA) relations
• Structural Ambiguity Decisions (work with Preslav
  Nakov)
• PP-attachment
• Noun compound bracketing
• Coordination grouping

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Semantic Relation Detection

• Goal automatically augment a lexical database
• Many potential relation types
• ISA (hypernymy/hyponymy)
• Part-Of (meronymy)
• Idea find unambiguous contexts which (nearly)
  always indicate the relation of interest

18
Lexico-Syntactic Patterns
19
Lexico-Syntactic Patterns
20
Adding a New Relation
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Semantic Relation Detection

• Lexico-syntactic Patterns
• Should occur frequently in text
• Should (nearly) always suggest the relation of
  interest
• Should be recognizable with little pre-encoded
  knowledge.
• These patterns have been used extensively by
  other researchers.

22
Structural Ambiguity Problems

• Apply the U U U idea to structural ambiguity
• Noun compound bracketing
• Prepositional Phrase attachment
• Noun Phrase coordination
• Motivation BioText project
• In eukaryotes, the key to transcriptional
  regulation of the Heat Shock Response is the Heat
  Shock Transcription Factor (HSF).
• Open-labeled long-term study of the subcutaneous
  sumatriptan efficacy and tolerability in acute
  migraine treatment.
• BimL protein interact with Bcl-2 or Bcl-XL, or
  Bcl-w proteins (Immuno-precipitation (anti-Bcl-2
  OR Bcl-XL or Bcl-w)) followed by Western blot
  (anti-EEtag) using extracts human 293T cells
  co-transfected with EE-tagged BimL and (bcl-2 or
  bcl-XL or bcl-w) plasmids)

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Applying U U U to Structural Ambiguity

• We introduce the use of (nearly) unambiguous
  features
• surface features
• Paraphrases
• Combined with very, very large corpora
• Achieve state-of-the-art results without labeled
  examples.
• Joint work with Preslav Nakov

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Noun Compound Bracketing

• (a) liver cell antibody (left
  bracketing)
• (b) liver cell line (right
  bracketing)
• In (a), the antibody targets the liver cell.
• In (b), the cell line is derived from the liver.

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Dependency Model

• right bracketing w1w2w3
• w2w3 is a compound (modified by w1)
• home health care
• w1 and w2 independently modify w3
• adult male rat
• left bracketing w1w2 w3
• only 1 modificational choice possible
• law enforcement officer

w1 w2 w3
w1 w2 w3
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Related Work

• Marcus(1980), Pustejoskyal.(1993), Resnik(1993)
• adjacency model Pr(w1w2) vs. Pr(w2w3)
• Lauer (1995)
• dependency model Pr(w1w2) vs. Pr(w1w3)
• Keller Lapata (2004)
• use the Web
• unigrams and bigrams
• Girju al. (2005)
• supervised model
• bracketing in context
• requires WordNet senses
• to be given

• Our approach
• Web as data
• ?2 , n-grams
• paraphrases
• surface features

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Computing Bigram Statistics

• Dependency Model, Frequencies
• Compare (w1,w2) to (w1,w3)
• Dependency model, Probabilities
• Pr(left) Pr(w1?w2w2)Pr(w2?w3w3)
• Pr(right) Pr(w1?w3w3)Pr(w2?w3w3)
• So we compare Pr(w1?w2w2) to Pr(w1?w3w3)

right
w1 w2 w3
left
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Probabilities Estimation

• Using page hits as a proxy for n-gram counts
• Pr(w1?w2w2) (w1,w2) / (w2)
• (w2) word frequency query for w2
• (w1,w2) bigram frequency query for w1 w2
• smoothed by 0.5

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Association Models ?2 (Chi Squared)

• A (wi,wj)
• B (wi) (wi,wj)
• C (wj) (wi,wj)
• D N (ABC)
• N 8 trillion ( ABCD)

8 billion Web pages x 1,000 words
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Web-derived Surface Features

• Authors often disambiguate noun compounds using
  surface markers, e.g.
• amino-acid sequence ? left
• brain stems cell ? left
• brains stem cell ? right
• The enormous size of the Web makes these frequent
  enough to be useful.

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Web-derived Surface FeaturesDash (hyphen)

• Left dash
• cell-cycle analysis ? left
• Right dash
• donor T-cell ? right
• fiber optics-system ? should be left..
• Double dash
• T-cell-depletion ? unusable

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Web-derived Surface FeaturesPossessive Marker

• Attached to the first word
• brains stem cell ? right
• Attached to the second word
• brain stems cell ? left
• Combined features
• brains stem-cell ? right

33
Web-derived Surface FeaturesCapitalization

• dont-care lowercase uppercase
• Plasmodium vivax Malaria ? left
• plasmodium vivax Malaria ? left
• lowercase uppercase dont-care
• brain Stem cell ? right
• brain Stem Cell ? right
• Disable this on
• Roman digits
• Single-letter words e.g. vitamin D deficiency

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Web-derived Surface FeaturesEmbedded Slash

• Left embedded slash
• leukemia/lymphoma cell ? right

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Web-derived Surface FeaturesParentheses

• Single-word
• growth factor (beta) ? left
• (brain) stem cell ? right
• Two-word
• (growth factor) beta ? left
• brain (stem cell) ? right

36
Web-derived Surface FeaturesComma, dot,
semi-colon

• Following the first word
• home. health care ? right
• adult, male rat ? right
• Following the second word
• health care, provider ? left
• lung cancer patients ? left

37
Web-derived Surface FeaturesDash to External
Word

• External word to the left
• mouse-brain stem cell ? right
• External word to the right
• tumor necrosis factor-alpha ? left

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Web-derived Surface FeaturesProblems Solutions

• Problem search engines ignore punctuation in
  queries
• brain-stem cell does not work
• Solution
• query for brain stem cell
• obtain 1,000 document summaries
• scan for the features in these summaries

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Other Web-derived FeaturesPossessive Marker

• We can also query directly for possessives
• Yes, brain stems cell sort of works.
• Search engines
• drop the possessive marker
• but s is kept
• Still, we cannot query for brain stems cell

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Other Web-derived FeaturesAbbreviation

• After the second word
• tumor necrosis factor (NF) ? right
• After the third word
• tumor necrosis (TN) factor ? right
• We query for, e.g., tumor necrosis tn factor
• Problems
• Roman digits IV, VI
• States CA
• Short words me

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Other Web-derived FeaturesConcatenation

• Consider health care reform
• healthcare 79,500,000
• carereform 269
• healthreform 812
• Adjacency model
• healthcare vs. carereform
• Dependency model
• healthcare vs. healthreform
• Triples
• healthcare reform vs. health carereform

42
Other Web-derived FeaturesUsing Googles

• Each allows a one-word wildcard
• Single star
• health care reform ? left
• health care reform ? right
• More stars and/or reverse order
• care reform health ? right

43
Other Web-derived FeaturesReorder

• Reorders for health care reform
• care reform health ? right
• reform health care ? left

44
Other Web-derived FeaturesInternal Inflection
Variability

• Vary inflection of second word
• tyrosine kinase activation
• tyrosine kinases activation

45
Other Web-derived FeaturesSwitch The First Two
Words

• Predict right, if we can reorder
• adult male rat as
• male adult rat

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Paraphrases

• The semantics of a noun compound is often made
  overt by a paraphrase (Warren,1978)
• Prepositional
• stem cells in the brain ? right
• cells from the brain stem ? right
• Verbal
• virus causing human immunodeficiency ? left
• pain associated with arthritis migraine ? right
• Copula
• office building that is a skyscraper ? right

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Paraphrases

• Lauer(1995), KellerLapata(2003), Girjual.
  (2005) predict NC semantics by choosing the most
  likely preposition
• of, for, in, at, on, from, with, about, (like)
• This could be problematic, when more than one
  preposition is possible
• In contrast
• we try to predict syntax, not semantics
• we do not disambiguate, just add up all counts
• cells in (the) bone marrow ? left
• cells from (the) bone marrow ? left

48
Paraphrases

• prepositional paraphrases
• We use 150 prepositions
• verbal paraphrases
• We use associated with, caused by, contained in,
  derived from, focusing on, found in, involved in,
  located at/in, made of, performed by, preventing,
  related to and used by/in/for.
• copula paraphrases
• We use is/was and that/which/who
• optional elements
• articles a, an, the
• quantifiers some, every, etc.
• pronouns this, these, etc.

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Evaluation Datasets

• Lauer Set
• 244 noun compounds (NCs)
• from Groliers encyclopedia
• inter-annotator agreement 81.5
• Biomedical Set
• 430 NCs
• from MEDLINE
• inter-annotator agreement 88 (? .606)

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Evaluation Experiments

• Exact phrase queries
• Limited to English
• Inflections
• Lauer Set Carrolls morphological tools
• Biomedical Set UMLS Specialist Lexicon

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Co-occurrence Statistics

• Lauer set

• Bio set

52
Paraphrase and Surface Features Performance

• Lauer Set
• Biomedical Set

53
Individual Surface Features Performance Bio
54
Individual Surface Features Performance Bio
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Results Lauer
56
Results Comparing with Others
57
Results Bio
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Results for Noun Compound Bracketing

• Introduced search engine statistics that go
  beyond the n-gram (applicable to other tasks)
• surface features
• paraphrases
• Obtained new state-of-the-art results on NC
  bracketing
• more robust than Lauer (1995)
• more accurate than KellerLapata (2004)

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Prepositional Phrase Attachment

• (a) Peter spent millions of dollars. (noun
  attach)
• (b) Peter spent time with his family. (verb
  attach)
• quadruple (v, n1, p, n2)
• (a) (spent, millions, of, dollars)
• (b) (spent, time, with, family)

60
Related Work

• Supervised
• (Brill Resnik, 94) transformation-based
  learning, WordNet classes, P82
• (Ratnaparkhi al., 94)
• ME, word classes (MI), P81.6
• (Collins Brooks, 95)
• back-off, P84.5
• (Stetina Makoto, 97) decision trees, WordNet,
  P88.1
• (Toutanova al., 04) morphology, syntax,
  WordNet, P87.5

• Unsupervised
• (Hindle Rooth, 93) partially parsed corpus,
  lexical associations over subsets of (v,n1,p),
  P80,R80
• (Ratnaparkhi, 98) POS tagged corpus, unambiguous
  cases for (v,n1,p), (n1,p,n2), classifier
  P81.9
• (Pantel Lin,00) collocation database,
  dependency parser, large corpus (125M words),
  P84.3

Unsup. state-of-the-art
61
PP-attachment Our Approach

• Unsupervised
• (v,n1,p,n2) quadruples, Ratnaparkhi test set
• Google and MSN Search
• Exact phrase queries
• Inflections WordNet 2.0
• Adding determiners where appropriate
• Models
• n-gram association models
• Web-derived surface features
• paraphrases

62
N-gram models

• (i) Pr(pn1) vs. Pr(pv)
• (ii) Pr(p,n2n1) vs. Pr(p,n2v)
• I eat/v spaghetti/n1 with/p a fork/n2.
• I eat/v spaghetti/n1 with/p sauce/n2.
• Pr or (frequency)
• smoothing as in (Hindle Rooth, 93)
• back-off from (ii) to (i)
• N-grams unreliable, if n1 or n2 is a pronoun.
• MSN Search no rounding of n-gram estimates

63
Web-derived Surface Features
P R

• Example features
• open the door / with a key ? verb (100.00,
  0.13)
• open the door (with a key) ? verb (73.58,
  2.44)
• open the door with a key? verb (68.18,
  2.03)
• open the door , with a key ? verb (58.44,
  7.09)
• eat Spaghetti with sauce ? noun (100.00,
  0.14)
• eat ? spaghetti with sauce? noun (83.33,
  0.55)
• eat , spaghetti with sauce ? noun (65.77,
  5.11)
• eat spaghetti with sauce ? noun (64.71,
  1.57)
• Summing achieves high precision, low recall.

sum
compare
sum
64
Paraphrases

• v n1 p n2
• v n2 n1 (noun)
• v p n2 n1 (verb)
• p n2 v n1 (verb)
• n1 p n2 v (noun)
• v PRONOUN p n2 (verb)
• BE n1 p n2 (noun)

65
Evaluation

• Ratnaparkhi dataset
• 3097 test examples, e.g.
• prepare dinner for family V
• shipped crabs from province V
• n1 or n2 is a bare determiner 149 examples
• problem for unsupervised methods
• left chairmanship of the N
• is the of kind N
• acquire securities for an N
• special symbols , /, etc. 230 examples
• problem for Web queries
• buy for 10 V
• beat SP-down from V
• is 43-owned by firm N

66
Results
For prepositions other then OF. (of ? noun
attachment)
Models in bold are combined in a majority vote.
Simpler but not significantly different from
84.3 (PantelLin,00).
67
Noun Phrase Coordination

• (Modified) real sentence
• The Department of Chronic Diseases and Health
  Promotion leads and strengthens global efforts to
  prevent and control chronic diseases or
  disabilities and to promote health and quality of
  life.

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NC coordination ellipsis

• Ellipsis
• car and truck production
• means car production and truck production
• No ellipsis
• president and chief executive
• All-way coordination
• Securities and Exchange Commission

69
NC Coordination ellipsis

• Quadruple (n1,c,n2,h)
• Penn Treebank annotations
• ellipsis
• (NP car/NN and/CC truck/NN production/NN).
• no ellipsis
• (NP (NP president/NN) and/CC (NP chief/NN
  executive/NN))
• all-way can be annotated either way
• This is a problem a parser must deal with.

Collins parser always predicts ellipsis, but
other parsers (e.g. Charniaks) try to solve it.
70
Related Work

• (Resnik, 99) similarity of form and meaning,
  conceptual association, decision tree, P80,
  R100
• (Rus al., 02) deterministic, rule-based
  bracketing in context, P87.42, R71.05
• (Chantree al., 05) distributional similarities
  from BNC, Sketch Engine (freqs., object/modifier
  etc.), P80.3, R53.8

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N-gram models

• (n1,c,n2,h)
• (i) (n1,h) vs. (n2,h)
• (ii) (n1,h) vs. (n1,c,n2)

72
Surface Features
sum
compare
sum
73
Paraphrases

• n1 c n2 h
• n2 c n1 h (ellipsis)
• n2 h c n1 (NO ellipsis)
• n1 h c n2 h (ellipsis)
• n2 h c n1 h (ellipsis)

74
Results428 examples from Penn TB
75
Conclusions

• Tapping the potential of very large corpora for
  unsupervised algorithms
• Go beyond n-grams
• Surface features
• Paraphrases
• Results competitive with best unsupervised
• Results can rival supervised algorithms
• Future Work
• Unambiguous Unlimited Unsupervised
• How to extend to other problems?

76
Thank you!

• http//biotext.berkeley.edu
• Supported in part by NSF DBI-0317510

77
What about Search?

• Web search currently does not use very much
  language analysis.
• Queries are very short (2.1 words/avg) so most
  queries match many pages
• Improvements in ranking make use of the massive
  size of the web
• Anchor text (words on links pointed to pages)
• Which hits users clicked on (starting to use
  this)
• As well as the structure of language
• Where query terms occur (title, etc)
• How close together query words occur

78
Using n-grams to make predictions

• Say trying to distinguish
• home health care
• home health care
• Main idea compare these co-occurrence
  probabilities
• home health vs
• health care

79
Using n-grams to make predictions

• Use search engines page hits as a proxy for
  n-gram counts
• compare Pr(w1?w2w2) to Pr(w1?w3w3)
• Pr(w1 ?w2w2 ) (w1,w2) / (w2)
• (w2) word frequency query for w2
• (w1,w2) bigram frequency query for w1 w2

80
Probabilities Why? (1)

• Why should we use
• (a) Pr(w1?w2w2), rather than
• (b) Pr(w2?w1w1)?
• KellerLapata (2004) calculate
• AltaVista queries
• (a) 70.49
• (b) 68.85
• British National Corpus
• (a) 63.11
• (b) 65.57

81
Probabilities Why? (2)

• Why should we use
• (a) Pr(w1?w2w2), rather than
• (b) Pr(w2?w1w1)?
• Maybe to introduce a bracketing prior.
• Just like Lauer (1995) did.
• But otherwise, no reason to prefer either one.
• Do we need probabilities? (association is OK)
• Do we need a directed model? (symmetry is OK)

82
Adjacency Dependency (2)

• right bracketing w1w2w3
• w2w3 is a compound (modified by w1)
• w1 and w2 independently modify w3
• adjacency model
• Is w2w3 a compound?
• (vs. w1w2 being a compound)
• dependency model
• Does w1 modify w3?
• (vs. w1 modifying w2)

w1 w2 w3
w1 w2 w3
w1 w2 w3
83
Paraphrases pattern (1)

• v n1 p n2 ? v n2 n1 (noun)
• Can we turn n1 p n2 into a noun compound n2
  n1?
• meet/v demands/n1 from/p customers/n2 ?
• meet/v the customer/n2 demands/n1
• Problem ditransitive verbs like give
• gave/v an apple/n1 to/p him/n2 ?
• gave/v him/n2 an apple/n1
• Solution
• no determiner before n1
• determiner before n2 is required
• the preposition cannot be to

84
Paraphrases pattern (2)

• v n1 p n2 ? v p n2 n1 (verb)
• If p n2 is an indirect object of v, then it
  could be switched with the direct object n1.
• had/v a program/n1 in/p place/n2 ?
• had/v in/p place/n2 a program/n1

Determiner before n1 is required to prevent n2
n1 from forming a noun compound.
85
Paraphrases pattern (3)

• v n1 p n2 ? p n2 v n1 (verb)
• indicates a wildcard position (up to three
  intervening words are allowed)
• Looks for appositions, where the PP has moved in
  front of the verb, e.g.
• I gave/v an apple/n1 to/p him/n2 ?
• to/p him/n2 I gave/v an apple/n1

86
Paraphrases pattern (4)

• v n1 p n2 ? n1 p n2 v (noun)
• Looks for appositions, where n1 p n2 has moved
  in front of v
• shaken/v confidence/n1 in/p markets/n2 ?
• confidence/n1 in/p markets/n2 shaken/v

87
Paraphrases pattern (5)

• v n1 p n2 ? v PRONOUN p n2 (verb)
• n1 is a pronoun ? verb (HindleRooth, 93)
• Pattern (5) substitutes n1 with a dative pronoun
  (him or her), e.g.
• put/v a client/n1 at/p odds/n2 ?
• put/v him at/p odds/n2

pronoun
88
Paraphrases pattern (6)

• v n1 p n2 ? BE n1 p n2 (noun)
• BE is typically used with a noun attachment
• Pattern (6) substitutes v with a form of to be
  (is or are), e.g.
• eat/v spaghetti/n1 with/p sauce/n2 ?
• is spaghetti/n1 with/p sauce/n2

to be