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Computational Tools for Linguists . Inderjeet Mani Georgetown University Topics. Computational tools for manual and automatic annotation of linguistic data exploration of linguistic hypotheses Case studies Demonstrations and training Inter-annotator reliability

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computational tools for linguists

Computational Tools for Linguists

Inderjeet Mani

Georgetown University

  • Computational tools for
    • manual and automatic annotation of linguistic data
    • exploration of linguistic hypotheses
  • Case studies
  • Demonstrations and training
  • Inter-annotator reliability
  • Effectiveness of annotation scheme
  • Costs and tradeoffs in corpus preparation


Data sparseness

Chomsky’s Critique


Mutual Information

Part-of-speech tagging

Annotation Issues

Inter-Annotator Reliability

Named Entity Tagging

Relationship Tagging

Case Studies


adjective ordering

Discourse markers: then


corpus linguistics
Corpus Linguistics
  • Use of linguistic data from corpora to test linguistic hypotheses => emphasizes language use
  • Uses computers to do the searching and counting from on-line material
    • Faster than doing it by hand! Check?
  • Most typical tool is a concordancer, but there are many others!
  • Tools can analyze a certain amount, rest is left to human!
  • Corpus Linguistics is also a particular approach to linguistics, namely an empiricist approach
    • Sometimes (extreme view) opposed to the rationalist approach, at other times (more moderate view) viewed as complementary to it
    • Cf. Theoretical vs. Applied Linguistics
empirical approaches in computational linguistics
Empirical Approaches in Computational Linguistics
  • Empiricism – the doctrine that knowledge is derived from experience
  • Rationalism: the doctrine that knowledge is derived from reason
  • Computational Linguistics is, by necessity, focused on ‘performance’, in that naturally occurring linguistic data has to be processed
    • Naturally occurring data is messy! This means we have to process data characterized by false starts, hesitations, elliptical sentences, long and complex sentences, input that is in a complex format, etc.
  • The methodology used is corpus-based
    • linguistic analysis (phonological, morphological, syntactic, semantic, etc.) carried out on a fairly large scale
    • rules are derived by humans or machines from looking at phenomena in situ (with statistics playing an important role)
example metonymy
Example: metonymy
  • Metonymy: substituting the name of one referent for another
    • George W. Bush invaded Iraq
    • A Mercedes rear-ended me
  • Is metonymy involving institutions as agents more common in print news than in fiction?
    • “The X Vreporting”
      • Let’s start with: “The X said”
        • This pattern will provide a “handle” to identify the data
exploring corpora
Exploring Corpora
  • Datasets

  • Metonymy Test using Corpora

the x said from concordance data
‘The X said’ from Concordance data

The preference for metonymy in print news arises because of the need to

communicate Information from companies and governments.

chomsky s critique of corpus based methods
Chomsky’s Critique of Corpus-Based Methods

1. Corpora model performance, while linguistics is aimed at the explanation of competence

If you define linguistics that way, linguistic theories will never be able to deal with actual, messy data

Many linguists don’t find the competence-performance distinction to be clear-cut. Sociolinguists have argued that the variability of linguistic performance is systematic, predictable, and meaningful to speakers of a language.

Grammatical theories vary in where they draw the line between competence and performance, with some grammars (such as Halliday’s Systemic Grammar) organized as systems of functionally-oriented choices.

chomsky s critique concluded
Chomsky’s Critique (concluded)

2. Natural language is in principle infinite, whereas corpora are finite, so many examples will be missed

Excellent point, which needs to be understood by anyone working with a corpus.

But does that mean corpora are useless?

  • Introspection is unreliable (prone to performance factors, cf. only short sentences), and pretty useless with child data.
  • Also, insights from a corpus might lead to generalization/induction beyond the corpus– if the corpus is a good sample of the “text population”

3. Ungrammatical examples won’t be available in a corpus

Depends on the corpus, e.g., spontaneous speech, language learners, etc.

The notion of grammaticality is not that clear

    • Who did you see [pictures/?a picture/??his picture/*John’s picture] of?
    • ARG/ADJUNCT example
which words are the most frequent
Which Words are the Most Frequent?

Common Words in Tom Sawyer (71,730 words), from

Manning & Schutze p.21

Will these counts hold in a different corpus (and genre, cf. Tom)?

What happens if you have 8-9M words? (check usage demo!)

data sparseness
Many low-frequency words

Fewer high-frequency words.

Only a few words will have lots of examples.

About 50% of word types occur only once

Over 90% occur 10 times or less.

So, there is merit to Chomsky’s 2nd objection

Data Sparseness

Frequency of word types in

Tom Sawyer, from M&S 22.

zipf s law frequency is inversely proportional to rank
Zipf’s Law: Frequency is inversely proportional to rank

Empirical evaluation of Zipf’s Law on Tom Sawyer, from M&S 23.

illustration of zipf s law brown corpus from m s p 30
Illustration of Zipf’s Law (Brown Corpus, from M&S p. 30)



  • See also
tokenizing words for corpus analysis
Tokenizing words for corpus analysis
  • 1. Break on
    • Spaces? 犬に当る男の子は私の兄弟である。

inuo butta otokonokowa otooto da

    • Periods? (U.K. Products)
    • Hyphens? data-base = database = data base
    • Apostrophes? won’t, couldn’t, O’Riley, car’s
  • 2. should different word forms be counted as distinct?
    • Lemma: a set of lexical forms having the same stem, the same pos, and the same word-sense. So, cat and cats are the same lemma.
    • Sometimes, words are lemmatized by stemming, other times by morphological analysis, using a dictionary and/or morphological rules
  • 3. fold case or not (usually folded)?
    • The the THEMark versus mark
    • One may need, however, to regenerate the original case when presenting it to the user
counting word tokens vs word types
Counting: Word Tokens vs Word Types
  • Word tokens in Tom Sawyer: 71,370
  • Word types: (i.e., how many different words) 8,018
  • In newswire text of that number of tokens, you would have 11,000 word types. Perhaps because Tom Sawyer is written in a simple style.
inspecting word frequencies in a corpus
Inspecting word frequencies in a corpus
  • Usage demo:
  • Sequences of linguistic items of length n
  • See
a test for association strength mutual information
A test for association strength: Mutual Information

Data from (Church et al. 1991)

1988 AP corpus; N=44.3M

interpreting mutual information
Interpreting Mutual Information
  • High scores, e.g., strong supporter (8.85) indicates strongly associated in the corpus

MI is a logarithmic score. To convert it, recall that X=2 log2X

so, 28.85 461.44. So this is 461 X chance.

  • Low scores – powerful support (1.74): this is 3X chance, since 21.74 3

I fxy fx fy x y

1.74 2 1984 13,428 powerful support

I = log2 (2N/1984*13428) = 1.74

  • So, doesn’t necessarily mean weakly associated – could be due to data sparseness
mutual information over grammatical relations
Mutual Information over Grammatical Relations
  • Parse a corpus
  • Determine subject-verb-object triples
  • Identify head nouns of subject and object NPs
  • Score subj-verb and verb-obj associations using MI
demo of verb subj verb obj parses
Demo of Verb-Subj, Verb-Obj Parses
  • Who devoursor what gets devoured?
  • Demo:
mi over verb obj relations
MI over verb-obj relations
  • Data from (Church et al. 1991)
a subj verb mi example who does what in news
A Subj-Verb MI Example: Who does what in news?

executive police politician

reprimand 16.36 shoot 17.37 clamor 16.94

conceal 17.46 raid 17.65 jockey 17.53

bank 18.27 arrest 17.96 wrangle 17.59

foresee 18.85 detain 18.04 woo 18.92

conspire 18.91 disperse 18.14 exploit 19.57

convene 19.69 interrogate 18.36 brand 19.65

plead 19.83 swoop 18.44 behave 19.72

sue 19.85 evict 18.46 dare 19.73

answer 20.02 bundle 18.50 sway 19.77

commit 20.04 manhandle 18.59 criticize 19.78

worry 20.04 search 18.60 flank 19.87

accompany 20.11 confiscate 18.63 proclaim 19.91

own 20.22 apprehend 18.71 annul 19.91

witness 20.28 round 18.78 favor 19.92

Data from (Schiffman et al. 2001)

famous corpora
‘Famous’ Corpora
  • Must see:
  • Brown Corpus
  • British National Corpus
  • International Corpus of English
  • Penn Treebank
  • Lancaster-Oslo-Bergen Corpus
  • Canadian Hansard Corpus
  • U.N. Parallel Corpus
  • TREC Corpora
  • MUC Corpora
  • English, Arabic, Chinese Gigawords
  • Chinese, ArabicTreebanks
  • North American News Text Corpus
  • Multext East Corpus – ‘1984’ in multiple Eastern/Central European langauges
links to corpora
Links to Corpora
  • Corpora:
    • Linguistic Data Consortium (LDC)
    • Oxford Text Archive
    • Project Gutenberg
    • CORPORA list
  • Other:
    • Chris Manning’s Corpora Page
    • Michael Barlow’s Corpus Linguistics page
    • Cathy Ball’s Corpora tutorial
summary introduction
Summary: Introduction
  • Concordances and corpora are widely used and available, to help one to develop empirically-based linguistic theories and computer implementations
  • The linguistic items that can be counted are many, but “words” (defined appropriately) are basic items
  • The frequency distribution of words in any natural language is Zipfian
    • Data sparseness is a basic problem when using observations in a corpus sample of language
  • Sequences of linguistic items (e.g., word sequences – n-grams) can also be counted, but the counts will be very rare for longer items
  • Associations between items can be easily computed
    • e.g., associations between verbs and parser-discovered subjs or objs


Data sparseness

Chomsky’s Critique


Mutual Information

Part-of-speech tagging

Annotation Issues

Inter-Annotator Reliability

Named Entity Tagging

Relationship Tagging

Case Studies


adjective ordering

Discourse markers: then


using pos in concordances
Using POS in Concordances

deal is more often a verb

In Fiction 2000

deal is more often a noun

in English Gigaword

deal is more prevalent in

Fiction 2000 than Gigaword

pos tagging what is it
POS Tagging – What is it?
  • Given a sentence and a tagset of lexical categories, find the most likely tag for each word in the sentence
  • Tagset – e.g., Penn Treebank (45 tags, derived from the 87-tag Brown corpus tagset)
  • Note that many of the words may have unambiguous tags
  • Example

Secretariat/NNP is/VBZ expected/VBNto/TO race/VB tomorrow/NN

People/NNS continue/VBP to/TOinquire/VB the/DT reason/NN for/IN the/DT race/NN for/IN outer/JJ space/NN

more details of pos problem
More details of POS problem
  • How ambiguous?
    • Most words in English have only one Brown Corpus tag
      • Unambiguous (1 tag) 35,340 word types
      • Ambiguous (2- 7 tags) 4,100 word types = 11.5%
        • 7 tags: 1 word type “still”
    • But many of the most common words are ambiguous
      • Over 40% of Brown corpus tokens are ambiguous
  • Obvious strategies may be suggested based on intuition
      • to/TO race/VB
      • the/DT race/NN
      • will/MD race/NN
  • Sentences can also contain unknown words for which tags have to be guessed: Secretariat/NNP is/VBZ
different english part of speech tagsets
Different English Part-of-Speech Tagsets
  • Brown corpus - 87 tags
    • Allows compound tags
      • “I'm” tagged as PPSS+BEM
        • PPSS for "non-3rd person nominative personal pronoun" and BEM for "am, 'm“
  • Others have derived their work from Brown Corpus
    • LOB Corpus: 135 tags
    • Lancaster UCREL Group: 165 tags
    • London-Lund Corpus: 197 tags.
    • BNC – 61 tags (C5)
    • PTB – 45 tags
  • To see comparisons ad mappings of tagsets, go to
ptb tagset development
PTB Tagset Development
  • Several changes were made to Brown Corpus tagset:
    • Recoverability
      • Lexical: Same treatment of Be, do, have, whereas BC gave each its own symbol
        • Do/VB does/VBZ did/VBD doing/VBG done/VBN
      • Syntactic: Since parse trees were used as part of Treebank, conflated certain categories under the assumption that they would be recoverable from syntax
        • subject vs. object pronouns (both PP)
        • subordinating conjunctions vs. prepositions on being informed vs. on the table (both IN)
        • Preposition “to” vs. infinitive marker (both TO)
    • Syntactic Function
      • BC: the/DT one/CD vs. PTB: the/DT one/NN
      • BC: both/ABX vs.
      • PTB: both/PDT the boys, the boys both/RB, both/NNS of the boys, both/CC boys and girls
ptb tagging process
PTB Tagging Process
  • Tagset developed
  • Automatic tagging by rule-based and statistical pos taggers
  • Human correction using an editor embedded in Gnu Emacs
  • Takes under a month for humans to learn this (at 15 hours a week), and annotation speeds after a month exceed 3,000 words/hour
  • Inter-annotator disagreement (4 annotators, eight 2000-word docs) was 7.2% for the tagging task and 4.1% for the correcting task
  • Manual tagging took about 2X as long as correcting, with about 2X the inter-annotator disagreement rate and an error rate that was about 50% higher.
  • So, for certain problems, having a linguist correct automatically tagged output is far more efficient and leads to better reliability among linguists compared to having them annotate the text from scratch!
automatic pos tagging
Automatic POS tagging
a baseline strategy
Choose the most likely tag for each ambiguous word, independent of previous words

i.e., assign each token to the pos-category it occurred in most often in the training set

E.g., race – which pos is more likely in a corpus?

This strategy gives you 90% accuracy in controlled tests

So, this “unigram baseline” must always be compared against

A Baseline Strategy
beyond the baseline
Beyond the Baseline
  • Hand-coded rules
  • Sub-symbolic machine learning
  • Symbolic machine learning
machine learning
Machine Learning
  • Machines can learn from examples
  • Learning can be supervised or unsupervised
  • Given training data, machines analyze the data, and learn rules which generalize to new examples
  • Can be sub-symbolic (rule may be a mathematical function) –e.g. neural nets
  • Or it can be symbolic (rules are in a representation that is similar to representation used for hand-coded rules)
  • In general, machine learning approaches allow for more tuning to the needs of a corpus, and can be reused across corpora
a probabilistic approach to pos tagging
What you want to do is find the “best sequence” of pos-tags C=C1..Cn for a sentence W=W1..Wn.

(Here C1 is pos_tag(W1)).

In other words, find a sequence of pos tags Cthat maximizes P(C| W)

Using Bayes’ Rule, we can say

P(C| W) = P(W | C) * P(C) / P(W )

Since we are interested in finding the value of C which maximizes the RHS, the denominator can be discarded, since it will be the same for every C

So, the problem is: Find C which maximizes

P(W | C) * P(C)

Example: He will race

Possible sequences:

He/PP will/MD race/NN

He/PP will/NN race/NN

He/PP will/MD race/VB

He/PP will/NN race/VB

W = W1 W2 W3

= He will race

C = C1 C2 C3






A Probabilistic Approach to POS tagging
independence assumptions
Independence Assumptions
  • P(C1….Cn) i=1, n P(Ci| Ci-1)
    • assumes that the event of a pos-tag occurring is independent of the event of any other pos-tag occurring, except for the immediately previous pos tag
      • From a linguistic standpoint, this seems an unreasonable assumption, due to long-distance dependencies
  • P(W1….Wn | C1….Cn) i=1, n P(Wi| Ci)
    • assumes that the event of a word appearing in a category is independent of the event of any other word appearing in a category
      • Ditto
  • However, the proof of the pudding is in the eating!
    • N-gram models work well for part-of-speech tagging
a statistical method for pos tagging




















A Statistical Method for POS Tagging


he 0 0 0 .3

will .8 .2 0 0

race 0 .4 .6 0

Find the value of C1..Cn which maximizes:

i=1, n P(Wi| Ci) * P(Ci| Ci-1)

Pos bigram


lexical generation


lexical generation probs


MD .4 .6

NN .3 .7

PP .8 .2


pos bigram probs

finding the best path through an hmm
Score(I) = Max J pred I [Score(J)* transition(I|J)]* lex(I)

Score(B) = P(PP|)* P(he|PP) =1*.3=.3

Score(C)=Score(B) *P(MD|PP) * P(will|MD) = .3*.8*.8= .19

Score(D)=Score(B) *P(NN|PP) * P(will|NN) = .3*.2*.2= .012

Score(E) = Max [Score(C)*P(NN|MD), Score(D)*P(NN|NN)] *P(race|NN) =

Score(F) = Max [Score(C)*P(VB|MD), Score(D)*P(VB|NN)]*P(race|VB)=

Finding the best path through an HMM




























but data sparseness bites again
But Data Sparseness Bites Again!
  • Lexical generation probabilities will lack observations for low-frequency and unknown words
  • Most systems do one of the following
    • Smooth the counts
      • E.g., add a small number to unseen data (to zero counts). For example, assume a bigram not seen in the data has a very small probability, e.g., .0001.
      • Backoff bigrams with unigrams, etc.
    • Use lots more data (you’ll still lose, thanks to Zipf!)
    • Group items into classes, thus increasing class frequency
      • e.g., group words into ambiguity classes, based on their set of tags. For counting, alll words in an ambiguity class are treated as variants of the same ‘word’
a symbolic learning method
A Symbolic Learning Method
  • HMMs are subsymbolic – they don’t give you rules that you can inspect
  • A method called Transformational Rule Sequence learning (Brill algorithm) can be used for symbolic learning (among other approaches)
  • The rules (actually, a sequence of rules) are learnt from an annotated corpus
  • Performs at least as accurately as other statistical approaches
  • Has better treatment of context compared to HMMs
    • rules which use the next (or previous) pos
      • HMMs just use P(Ci| Ci-1) or P(Ci| Ci-2Ci-1)
    • rules which use the previous (next) word
      • HMMs just use P(Wi|Ci)
brill algorithm overview
Assume you are given a training corpus G (for gold standard)

First, create a tag-free version V of it


As the algorithm proceeds, each successive rule becomes narrower (covering fewer examples, i.e., changing fewer tags), but also potentially more accurate

Some later rules may change tags changed by earlier rules

1. First label every word token in V with most likely tag for that word type from G. If this ‘initial state annotator’ is perfect, you’re done!

2. Then consider every possible transformational rule, selecting the one that leads to the most improvement in V using G to measure the error

3. Retag V based on this rule

4. Go back to 2, until there is no significant improvement in accuracy over previous iteration

Brill Algorithm (Overview)
brill algorithm detailed
1. Label every word token with its most likely tag (based on lexical generation probabilities).

2. List the positions of tagging errors and their counts, by comparing with ground-truth (GT)

3. For each error position, consider each instantiation I of X, Y, and Z in Rule template. If Y=GT, increment improvements[I], else increment errors[I].

4. Pick the I which results in the greatest error reduction, and add to output

e.g., VB NN PREV1OR2TAG DT improves 98 errors, but produces 18 new errors, so net decrease of 80 errors

5. Apply that I to corpus

6. Go to 2, unless stopping criterion is reached

Most likely tag:

P(NN|race) = .98

P(VB|race) = .02

Is/VBZ expected/VBN to/TO race/NNtomorrow/NN

Rule template: Change a word from tag X to tag Y when previous tag is Z

Rule Instantiation to above example: NN VB PREV1OR2TAG TO

Applying this rule yields:

Is/VBZ expected/VBN to/TO race/VB tomorrow/NN

Brill Algorithm (Detailed)
example of error reduction
Example of Error Reduction

From Eric Brill (1995):

Computational Linguistics, 21, 4, p. 7

example of learnt rule sequence
Example of Learnt Rule Sequence
    • to/TO race/NN->VB
    • might/MD vanish/VBP-> VB
    • might/MD not/MD reply/NN -> VB
    • the/DT great/JJ feast/VB->NN
    • He/PP was/VBZ killed/VBD->VBN by/IN Chapman/NNP
handling unknown words
Handling Unknown Words
  • Can also use the Brill method
  • Guess NNP if capitalized, NN otherwise.
  • Or use the tag most common for words ending in the last 3 letters.
  • etc.

Example Learnt Rule Sequence

for Unknown Words

pos tagging using unsupervised methods
Reason: Annotated data isn’t always available!

Example: the can

Let’s take unambiguous words from dictionary, and count their occurrences after the

the .. elephant

the .. guardian

Conclusion: immediately after the, nouns are more common than verbs or modals

Initial state annotator: for each word, list all tags in dictionary

Transformation template:

Change tag of word to tag Y if the previous (next) tag (word) is Z, where is a set of 2 or more tags

Don’t change any other tags

POS Tagging using Unsupervised Methods
error reduction in unsupervised method
Error Reduction in Unsupervised Method
  • Let a rule to change to Y in context C be represented as Rule(, Y, C).
    • Rule1: {VB, MD, NN}NNPREVWORD the
    • Rule2: {VB, MD, NN} VB PREVWORD the
  • Idea:
    • since annotated data isn’t available, score rules so as to prefer those where Y appears much more frequently in the context C than all others in 
      • frequency is measured by counting unambiguously tagged words
      • so, prefer {VB, MD, NN}NNPREVWORD the


since dict-unambiguous nouns are more common in a corpus after the than dict-unambiguous verbs

summary pos tagging
Summary: POS tagging
  • A variety of POS tagging schemes exist, even for a single language
  • Preparing a POS-tagged corpus requires, for efficiency, a combination of automatic tagging and human correction
  • Automatic part-of-speech tagging can use
    • Hand-crafted rules based on inspecting a corpus
    • Machine Learning-based approaches based on corpus statistics
      • e.g., HMM: lexical generation probability table, pos transition probability table
    • Machine Learning-based approaches using rules derived automatically from a corpus
  • Combinations of different methods often improve performance


Data sparseness

Chomsky’s Critique


Mutual Information

Part-of-speech tagging

Annotation Issues

Inter-Annotator Reliability

Named Entity Tagging

Relationship Tagging

Case Studies


adjective ordering

Discourse markers: then


adjective ordering
Adjective Ordering
  • *A political serious problem
  • *A social extravagant life
  • *red lovely hair
  • *old little lady
  • *green little men
  • Adjectives have been grouped into various classes to explain ordering phenomena
collins cobuild l2 grammar
Collins COBUILD L2 Grammar
  • qualitative < color < classifying
  • Qualitative – expresses a quality that someone or something has, e.g., sad, pretty, small, etc.
    • Qualitative adjectives are gradable, i.e., the person or thing can have more or less of the quality
  • Classifying – used to identify the class something belongs to, i.e.., distinguishing
    • financial help, American citizens.
    • Classifying adjectives aren’t gradable.
  • So, the ordering reduces to
    • Gradable < color < non-gradable
      • A serious political problem
      • Lovely red hair
      • Big rectangular green Chinese carpet
vendler 68
Vendler 68
  • A9 < A8 < …A2 < A1x <A1m < …<A1a
  • A9: probably, likely, certain
  • A8: useful, profitable, necessary
  • A7: possible, impossible
  • A6: clever, stupid, reasonable, nice, kind, thoughtful, considerate
  • A5: ready, willing, anxious
  • A4: easy
  • A3: slow, fast, good, bad, weak, careful, beautiful
  • A2: contrastive/polar adjectives: long-short, thick-thin, big-little, wide-narrow
  • A1j: verb-derivatives: washed
  • A1i: verb-derivatives: washing
  • A1h: luminous
  • A1g: rectangular
  • A1f: color adjectives
  • A1a: iron, steel, metal

big rectangular green Chinese carpet

other adjective ordering theories
Other Adjective Ordering Theories

Collins COBUILD: gradable < color < non-gradable

Goyvaerts, Q&G, Dixon: size < age < color

Goyvaerts, Q&G: color < denominal

Goyvaerts, Dixon: shape < color

testing the theories on large corpora
Testing the Theories on Large Corpora
  • Selective coverage of a particular language or (small) set of languages
  • Based on categories that aren’t defined precisely that are computable
  • Based on small large numbers of examples
  • Test gradable < color < non-gradable
computable tests for gradable adjectives
Computable Tests for Gradable Adjectives
  • Submodifiers expressing gradation
    • very|rather|somewhat|extremely A
      • But what about “very British”?

  • Periphrastic comparatives
    • “more A than“ | "the most A“
  • Inflectional comparatives
    • -er|-est

challenges data sparseness
Challenges: Data Sparseness
  • Data sparseness
    • Only some pairs will be present in a given corpus
      • few adjectives on the gradable list may be present
    • Even fewer longer sequences will be present in a corpus
      • Use transitivity?
        • small < red, red < wooden -->small < red < wooden?
challenges tool incompleteness
Challenges: Tool Incompleteness
  • Search pattern will return many non-examples
    • Collocations
      • common or marked ones
        • American “green card”
        • national Blue Cross
    • Adjective Modification
      • bright blue
    • POS-tagging errors
    • May also miss many examples
results from corpus analysis
Results from Corpus Analysis
  • G < C < not G generally holds
  • However, there are exceptions
    • Classifying/Non-Gradable < Color

After all, the maple leaf replaced the British red ensign as Canada's flag almost 30 years ago.

where he stood on a stage festooned with balloons displaying the Palestinian green, white and red flag

    • Color < Shape

paintings in which pink, roundish shapes, enriched with flocking, gel, lentils and thread, suggest the insides of the female body.

summary adjective ordering
Summary: Adjective Ordering
  • It is possible to test concrete predictions of a linguistic theory in a corpus-based setting
  • The testing means that the machine searches for examples satisfying patterns that the human specifies
  • The patterns can pre-suppose a certain/high degree of automatic tagging, with attendant loss of accuracy
  • The patterns should be chosen so that they provide “handles” to identify the phenomena of interest
  • The patterns should be restricted enough that the number of examples the human has to judge is not infeasible
  • This is usually an iterative process


Data sparseness

Chomsky’s Critique


Mutual Information

Part-of-speech tagging

Annotation Issues

Named Entity Tagging

Inter-Annotator Reliability

Relationship Tagging

Case Studies


adjective ordering

Discourse markers: then


the art of annotation 101
The Art of Annotation 101
  • Define Goal
  • Eyeball Data (with the help of Computers)
  • Design Annotation Scheme
  • Develop Example-based Guidelines
  • Unless satisfied/exhausted, goto 1
  • WriteTraining Manuals
  • Initiate HumanTraining Sessions
  • Annotate Data / Train Computers
      • Computers can also help with the annotation
  • Evaluate Humans and Computers
  • Unless satisfied/exhausted, goto 1
annottation methodology picture
Annottation Methodology Picture
























goals of an annotation scheme
Goals of an Annotation Scheme
  • Simplicity – simple enough for a human to carry out
  • Precision – precise enough to be useful in CLI applications
  • Text-based – annotation of an item should be based on information conveyed by the text, rather than information conveyed by background information
  • Human-centered – should be based on what a human can infer from the text, rather than what a machine can currently do or not do
  • Reproducible – your annotation should be reproducible by other humans (i.e., inter-annotator agreement should be high)
    • obviously, these other humans may have to have particular expertise and training
what should an annotation contain
What Should An Annotation Contain
  • Additional Information about the text being annotated – e.g., EAGLES external and internal criteria
  • Information about the annotator – who, when, what version of tool, etc. (usually in meta-tags associated with the text)
  • The tagged text itself
  • Example:
external and internal criteria eagles
External and Internal Criteria (EAGLES)
  • External: participants, occasion, social setting, communicative function
    • origin: Aspects of the origin of the text that are thought to affect its structure or content.
    • state: the appearance of the text, its layout and relation to non-textual matter, at the point when it is selected for the corpus.
    • aims: the reason for making the text and the intended effect it is expected to have.
  • Internal: patterns of language use
    • Topic (economics, sports, etc.)
    • Style (formal/informal, etc.)
external criteria state eagles
External Criteria – state (EAGLES)
  • Mode
    • spoken
      • participant awareness: surreptitious/warned/aware
      • venue: studio/on location/telephone
    • written
  • Relation to the medium
    • written: how it is laid out, the paper, print, etc.
    • spoken: the acoustic conditions, etc.
  • Relation to non-linguistic communicative matter
    • diagrams, illustrations, other media that are coupled with the language in a communicative event.
  • Appearance
    • e.g., advertising leaflets, aspects of presentation that are unique in design and are important enough to have an effect on the language.
examples of annotation schemes changing the way we do business
Examples of annotation schemes (changing the way we do business!)
  • POS tagging annotation – Penn Treebank Scheme
  • Named entity annotation – ACE Scheme
  • Phrase Structure annotation – Penn Treebank scheme
  • Time Expression annotation – TIMEX2 Scheme
  • Protein Name Annotation – GU Scheme
  • Event Annotation – TimeML Scheme
  • Rhetorical Structure Annotation - RST Scheme
  • Coreference Annotation, Subjectivity Annotation, Gesture Annotation, Intonation Annotation, Metonymy Annotation, etc., etc.
  • Etc.
  • Several hundred schemes exist, for different problems in different languages
pos tag formats non sgml to sgml
POS Tag Formats: Non-SGML – to SGML
  • CLAWS tagger: non-SGML
    • What_DTQ can_VM0 CLAWS_NN2 do_VDI to_PRP Inderjeet_NP0 's_POS noonsense_NN1 text_NN1 ?_?
  • Brill tagger: non-SGML
    • What/WP can/MD CLAWS/NNP do/VB to/TO Inderjeet/NNP 's/POS noonsense/NN text/NN ?/.
  • Alembic POS tagger:
    • <s><lex pos=WP>What</lex> <lex pos=MD>can</lex> <lex pos=NNP>CLAWS</lex> <lex pos=VB>do</lex> <lex pos=TO>to</lex> <lex pos=NNP>Inderjeet</lex> <lex pos=POS>'</lex><lex pos=PRP>s</lex> <lex pos=VBP>noonsense</lex> <lex pos=NN>text</lex> <lex pos=".">?</lex></s>
  • Conversion to SGML is pretty trivial in such cases
sgml standard generalized markup language
A general markup language for text

HTML is an instance of an SGML encoding

Text Encoding Initiative (TEI): defines SGML schemes for marking up humanities text resources as well as dictionaries


<p><s>I’m really hungry right now.</s><s>Oh, yeah?</s>

<utt speak=“Fred” date=“10-Feb-1998”>That is an ugly couch.</utt>

Note: some elements (e.g., <p>) can consist just of a single tag

Character references: ways of referring to the non-ASCII characters using a numeric code

&#229; (this is in decimal) &#xE5; (this is in hexadecimal)


Entity references: are used to encode a special character or sequence of characters via a symbolic name



SGML (Standard Generalized Markup Language)
A document type definition, or DTD, is used to define a grammar of legal SGML structures for a document

e.g., para should consist of one or more sentences and nothing else

SGML parser verifies that document is compliant with DTD

DTD’s can therefore be used for XML as well

DTDs can specify what attributes are required, in what order, what their legit values are, etc.

The DTDs are often ignored in practice!


<!ENTITY writer SYSTEM "">

<!ATTLIST payment type (check|cash) "cash">



<payment type="check">

  • “Extensible Markup Language (XML) is a simple, very flexible text format derived from SGML.
  • Originally designed to meet the challenges of large-scale electronic publishing, XML is also playing an increasingly important role in the exchange of a wide variety of data on the Web and elsewhere.”
  • Defines a simplified subset of SGML, designed especially for Web applications
  • Unlike HTML, separates out display (e.g., XSL) from content (XML)
  • Example

<p/><s><lex pos=“WP”>What</lex> <lex pos=“MD”>can</lex></s>

  • Makes use of DTDs, but also RDF Schemas
rdf schemas
RDF Schemas
  • Example of Real RDF Schema:
  • (see EVENT tag and attributes)
inline versus standoff annotation
Inline versus Standoff Annotation
  • Usually, when tags are added, an annotation tool is used, to avoid spurious insertions or deletions
  • The annotation tool may use inline or standoff annotation
  • Inline – tags are stored internally in (a copy of) the source text.
    • Tagged text can be substantially larger than original text
    • Web pages are a good example – i.e., HTML tags
  • Standoff – tags are stored internally in separate files, with information as to what positions in the source text the tags occupy
    • e.g., PERSON 335 337
    • However, the annotation tool displays the text as if the tags were in-line
summary annotation issues
Summary: Annotation Issues
  • A ‘best-practices’ methodology is widely used for annotating corpora
  • The annotation process involves computational tools at all stages
  • Standard guidelines are available for use
  • To share annotated corpora (and to ensure their survivability), it is crucial that the data be represented in a standard rather than ad hoc format
  • XML provides a well-established, Web-compliant standard for markup languages
  • DTDs and RDF provide mechanisms for checking well-formedness of annotation


Data sparseness

Chomsky’s Critique


Mutual Information

Part-of-speech tagging

Annotation Issues

Inter-Annotator Reliability

Named Entity Tagging

Relationship Tagging

Case Studies


adjective ordering

Discourse markers: then


  • Deborah Schiffrin. Anaphoric then: aspectual, textual, and epistemic meaning. Linguistics 30 (1992), 753-792
  • Schiffrin xamines uses of then in data elicited via 20 sociolinguistic interviews, each an hour long
  • Distinguishes two anaphoric temporal senses, showing that they are differentiated by clause position
  • Shows that they have systematic effects on aspectual interpretation
  • A parallel argument is made for two epistemic temporal senses
schiffrin temporal and non temporal senses
Schiffrin: Temporal and Non-Temporal Senses
  • Anaphoric Senses
    • ‘Narrative’ temporal sense (shifts reference time)
      • And then I uh lived there until I was sixteen
    • Continuing Temporal sense (continues a previous reference time)
      • I was only a little boy then.
  • Epistemic senses
    • Conditional ‘sentences’ (rare, but often have temporal antecedents in her data)
      • But if I think about it for a few days -- well, then I seem to remember a great deal
      • …if I’m still in the situation where I am now….I’m, not gonna have no more then
    • Initiation-response-evaluation sequences (‘in that case’?)
      • Freda: Do y’ still need the light?
      • Debby: Um.
      • Freda” W’ll have t’ go in then. Because the bugs are out.
schiffrin s argument simplified and its test
Schiffrin’s Argument (Simplified) and Its Test
  • Shifting RT thens (call these Narrative) & then in if-then conditionals
    • similar semantic function
    • mainly clause-initial
  • Continuing RT thens (call these Temporal) & IRE thens
    • similar semantic function
    • mainly clause final
    • stative verb more likely (since RT overlaps, verbs conveying duration are expected)
  • Call the rest Other
    • isn’t differentiated into if-then versus IRE
    • So, only part of her claims tested
so what do we do then
So, What do we do Then?
  • Define environments of interest, each one defined by a pattern
  • For each environment
    • Find examples matching the pattern
    • If classifying the examples is manageable, carry it out and stop
    • Otherwise restrict the environment by adding new elements to the pattern, and go back to 1
  • So, for each final environment, we claim that X% of the examples in that environment are of a particular class
  • Initial ‘then’ Pattern: (^|_CC|_RB)\s*then\w+\s+\w
  • Final ‘then’ Pattern: [^\,]\s+then[\.\?\'\;\!\:]
Non-Narrative Initial ‘then’

then there [be]

then come

then again

then and now

only then

even then

so then

Non-Temporal Final ‘then’

What then?

All right/OK [,] then

And then?

  • Other is a presence in final position in fiction and broadcast news, and in initial position in print news. Is this real or artifact of catch-all class?
  • Conclusion: only part of her claims tested. But those claims are borne out across three different genres and much more data!


Data sparseness

Chomsky’s Critique


Mutual Information

Part-of-speech tagging

Annotation Issues

Inter-Annotator Reliability

Named Entity Tagging

Relationship Tagging

Case Studies


adjective ordering

Discourse markers: then


considerations in inter annotator agreement
Considerations in Inter-Annotator Agreement
  • Size of tagset
  • Structure of tagset
  • Clarity of Guidelines
  • Number of raters
  • Experience of raters
  • Training of raters
    • Independent ratings (preferred)
    • Consensus (not preferred)
  • Exact, partial, and equivalent matches
  • Metrics
  • Lessons Learned: Disagreement patterns suggest guideline revisions
protein names
Considerable variability in the forms of the names

Multiple naming conventions

Researchers may name a newly discovered protein based on


sequence features

gene name

cellular location

molecular weight


or other properties

Prolific use of abbreviations and acronyms

fushi tarazu 1 factor homolog

Fushi tarazu factor (Drosophila) homolog 1

FTZ-F1 homolog ELP

steroid/thyroid/retinoic nuclear hormone receptor homolog nhr-35

V-INT 2 murine mammary tumor virus integration site oncogene homolog

fibroblast growth factor 1 (acidic) isoform 1 precursor

nuclear hormone receptor subfamily 5, Group A, member 1

Protein Names
example for f measure scorer output protein name tagging
Example for F-measure: Scorer Output (Protein Name Tagging)


CORR        FTZ-F1 homolog ELP   |           FTZ-F1 homolog ELP INCO              M2-LHX3 |                              M2SPUR             |                               -SPUR                                    |                            LHX3

Precision = ¼ = 0.25

Recall = ½ = 0.5

F-measure = 2 * ¼ * ½ / ( ¼ + ½ ) = 0.33

the importance of disagreement
The importance of disagreement
  • Measuring inter-annotator agreement is very useful in “debugging” the annotation scheme
  • Disagreement can lead to improvements in the annotation scheme
  • Extreme disagreement can lead to abandonment of the scheme
v2 assessment abs2
Old Guidelines

protein0.71 F

acronym0.85 F

array-protein0.15 F

New Guidelines

protein 0.86 F

long-form0.71 F

these are only ~4% of tags

V2 Assessment (ABS2)
timex2 annotation scheme
TIMEX2 Annotation Scheme

Time Points <TIMEX2 VAL="2000-W42">the third week of October</TIMEX2>

Durations <TIMEX2 VAL=“PT30M”>half an hour long</TIMEX2>

Indexicality <TIMEX2 VAL=“2000-10-04”>tomorrow</TIMEX2>


Fuzziness <TIMEX2 VAL=“1990-SU”>Summer of 1990 </TIMEX2>

<TIMEX2 VAL=“1999-07-15TMO”>This morning</TIMEX2>

Non-specificity <TIMEX2 VAL="XXXX-04" NON_SPECIFIC=”YES”>April</TIMEX2> is usually wet.

For guidelines, tools, and corpora, please see

timex2 inter annotator agreement
TIMEX2 Inter-Annotator Agreement

193 NYT news docs

5 annotators

10 pairs of annotators

  • Human annotation quality is ‘acceptable’ on EXTENT and VAL
  • Poor performance on Granularity and Non-Specific
    • But only a small number of instances of these (200 ~ 6000)
  • Annotators deviate from guidelines, and produce systematic errors (fatigue?)
    • several years ago: PXY instead of PAST_REF
    • all day: P1D instead of YYYY-MM-DD
summary inter annotator reliability
Summary: Inter-Annotator Reliability
  • There’s no point going on with an annotation scheme if it can’t be reproduced
  • There are standard methods for measuring inter-annotator reliability
  • An analysis of inter-annotator disagreements is critical for “debugging” an annotation scheme


Data sparseness

Chomsky’s Critique


Mutual Information

Part-of-speech tagging

Annotation Issues

Inter-Annotator Reliability

Named Entity Tagging

Relationship Tagging

Case Studies


adjective ordering

Discourse markers: then


information extraction
Information Extraction
  • Types
    • Flag names of people, organizations, places,…
    • Flag and normalize time expressions, phrases such as time expressions, measure phrases, currency expressions, etc.
    • Group coreferring expressions together
    • Find relations between named entities (works for, located at, etc.)
    • Find events mentioned in the text
    • Find relations between events and entities
    • A hot commercial technology!
  • Example patterns:
    • Mr. ---,
    • , Ill.
message understanding conferences mucs
Message Understanding Conferences (MUCs)
  • Idea: precise tasks to measure success, rather than test suite of input and logical forms.
  • MUC-1 1987 and MUC-2 1989 - messages about navy operations
  • MUC-3 1991 and MIC-4 1992 - news articles and transcripts of radio broadcasts about terrorist activity
  • MUC-5 1993 - news articles about joint ventures and microelectronics
  • MUC-6 1995 - news articles about management changes, + additional tasks of named entity recognition, coreference, and template element
  • MUC-7 1998 – mostly multilingual information extraction
  • Has also been applied to hundreds of other domains - scientific articles, etc., etc.
historical perspective
Historical Perspective
  • Until MUC-3 (1993), many IE systems used a Knowledge Engineering approach
    • They did something like full chart parsing with a unification-based grammar with full logical forms, a rich lexicon and KB
    • E.g., SRI’s Tacitus
  • Then, they discovered that things could work much faster using finite-state methods and partial parsing
  • And that using domain-specific rather than general purpose lexicons simplified parsing (less ambiguity due to fewer irrelevant senses)
  • And that these methods worked even better for the IE tasks
    • E.g., SRI’s Fastus, SRA’s Nametag
  • Meanwhile, people also started using statistical learning methods from annotated corpora
    • Including CFG parsing
an instantiated scenario template
An instantiated scenario template


Wall Street Journal, 06/15/88

MAXICARE HEALTH PLANS INC and UNIVERSAL HEALTH SERVICES INC have dissolved a joint venture which provided health services.

2002 automatic content extraction ace program entity types
2002 Automatic Content Extraction (ACE) Program: Entity Types
  • Person
  • Organization
  • (Place)
    • Location – e.g., geographical areas, landmasses, bodies of water, geological formations
    • Geo-Political Entity – e.g., nations, states, cities
      • Created due to metonymies involving this class of places
      • The riots in Miami
      • Miami imposed a curfew
      • Miami railed against a curfew
  • Facility – buildings, streets, airports, etc.
ace entity attributes and relations
ACE Entity Attributes and Relations
  • Attributes
    • Name: An entity mentioned by name
    • Pronoun
    • Nominal
  • Relations
    • AT: based-in, located, residence
    • NEAR: relative-location
    • PART: part-of, subsidiary, other
    • ROLE: affiliate-partner, citizen-of, client, founder, general-staff, manager, member, owner, other
    • SOCIAL: associate, grandparent, parent, sibling, spouse, other-relative, other-personal, other-professional
designing an information extraction task
Designing an Information Extraction Task
  • Define the overall task
  • Collect a corpus
  • Design an Annotation Scheme
    • linguistic theories help
  • Use Annotation Tools
    • - authoring tools
    • -automatic extraction tools
  • Apply to annotation to corpus, assessing reliability
  • Use training portion of corpus to train information extraction (IE) systems
  • Use test portion to test IE systems, using a scoring program
annotation tools
Annotation Tools
  • Specialized authoring tools used for marking up text without damaging it
  • Some tools are tied to particular annotation schemes
steps in information extraction
Steps in Information Extraction
  • Tokenization
    • Language Identification
    • Document Zoning
    • Sentence and Word Tokenization
  • Morphological and Lexical Processing
    • Tagging entities of interest
    • Specific trigger lexicons
    • Dealing with unknown words
    • Part-of-Speech Tagging
    • Word-Sense Tagging
    • Morphological Analysis
  • Parsing
    • Finite-State Parsing (usually just chunking)
  • Domain Semantics
    • Coreference
    • Merging Partial Results
morphological analysis
Morphological Analysis
  • Inflectional morphology, mostly
  • For simple languages (English, Japanese) – simple inflectional module suffices
  • For more complex languages (Spanish) – a finite-state transducer is used
  • For morphologically very complex languages (Arabic, Hebrew) – complex finite state transducer architectures
  • For languages with productive noun compounding (German) – specialized module needed
finite state parsing for ie
A.C. Nielesen CO.NGsaid VGGeorge GarrickNG, 40 years old, presidentNGof information Resources Inc.NG's London-based European Information Services operationNG, will becomeVGpresidentNGand chief operating officerNGof Nielsen Marketing Research USANG, a unit NG of Dun & Bradstree Corp. NG

First find NG, VG, particles; ignore PP attachment; ignore clause boundaries; maybe ignore modifiers that aren’t domain-relevant

Later transducers handle more complex phenomena:

relative clauses (e.g., look for second verb for marking end of rc; subject relatives: associate subject with first and second verb; object relatives: associate object with head noun before rel mod)

general clause segmentation



PP argument attachment (only for verbs important in domain whose subcat info is provided – rest are adverbial adjuncts)

Finite-State Parsing for IE
example text processing

Trigger word tagging

Named Entity tagging

Chunk parsing: NGs, VGs, preps, conjunctions

Bridgestone Sports Co.said Friday it has set up a joint ventureinTaiwanwith a local concern and a Japanese trading house to produce golf clubs to be shippedtoJapan.

Example Text Processing



The joint venture, Bridgestone Sports Taiwan Cp., capitalized at 20 million new Taiwan dollars, will start production in January 1990with production of 20,000 iron and “metal wood” clubs a month.

merging structures



Product: golf clubs


Bridgestone Sports Co. said Friday it has set up a joint venture in Taiwan with a local concern and a Japanese trading house to produce golf clubs to be shipped to Japan.

Merging Structures

The joint venture, Bridgestone Sports Taiwan Cp., capitalized at 20 million new Taiwan dollars, will start production in January 1990 with production of 20,000 iron and “metal wood” clubs a month.



Company: Bridgestone Sports Taiwan Co

Product: iron and “metal wood” clubs

Start-date: DURING 1990

  • Coreference means establishing referential relations between expressions.
    • Pronouns ..Mr. Gates …he, the testimony….it
    • Definite NPs Microsoft….the company
    • Indefinite NPs the building…an apartment
    • Proper Names Bill Gates…William Gates…. Mr. Gates
    • Temporal Expressions today, three weeks from Monday
    • Headless Determiners all, the one, five
    • Prenominals aluminum siding …the price of aluminum
    • Events they attacked at dawn…the attack
  • Types of relationships:
    • Identity, Part-whole
    • Set-subset the jurors…five ….
    • Set-member the jurors…on
statistical named entity tagging
Statistical Named Entity Tagging
  • Typically, treat it as a word-level tagging problem
    • To get phrase-level tags, one could greedily concatenate adjacent tags
      • this will fail to separate ‘like’ tags
  • Approaches can separately model words at start, end, or middle of name
    • BBN Identifinder does that

P(C|W) = P(W, C)/P(W)

 argmaxCP(W, C)

P(Ci|Ci-1, wi-1) first word in a name

* P(<w, f>i=first|Ci, Ci-1) first word in a name

* P(<w,f>i|<w,f>i-1, Ci) all but the first word in a name

Word features f includes information about capitalization, initials, etc.

information extraction metrics
Precision: Correct Answers/Answers Produced

Recall: Correct Answers /Total Possible Correct

F-measure - uses a parameter  to weight precision versus recall (=1 for balance)

F = (B2+1) PR / B2(P+R)

F =.6 for the relationship/event extraction task (ceiling) in MUC

F = .95+ for named entity task in MUC

= .8 or so for coreference task

Information Extraction Metrics
ie and qa evaluations
IE and QA Evaluations

Names in English

Names from audio @ 0%15% word error

Names in JapaneseNames in Chinese


Question Answering

Event extraction

Current status for various information extraction and question-answering components

summary information extraction
Summary: Information Extraction
  • A variety of IE tasks and methods are available
  • Named entities, relations, and event templates can be filled, as well as coreference relations
  • Linguistic information used can be hand-crafted or corpus-based
  • Domain knowledge, where needed, is hand-crafted
  • Performance on names is better than on relations, while “deep” templates have shown a 60% ceiling effect


Data sparseness

Chomsky’s Critique


Mutual Information

Part-of-speech tagging

Annotation Issues

Inter-Annotator Reliability

Named Entity Tagging

Relationship Tagging

Case Studies


adjective ordering

Discourse markers: then


motivation for temporal information extraction
Motivation for Temporal Information Extraction
  • Story Understanding
    • Question-answering
    • Summarization
  • Focus on temporal aspects of narrative
chronology of the marathon mini story










twist ankle



Chronology of ‘The Marathon’ (mini-story)

Yesterday Holly wasrunning a marathon whenshe twisted her ankle. David hadpushed her.

1. When did the running occur?


2. When did the twisting occur?

Yesterday, during the running.

3. Did the pushing occur before the twisting?


4. Did Holly keep running after twisting her ankle?

5. Maybe not????

factors influencing event ordering
Factors influencing Event Ordering

(1) Max entered the room. He had drunk a lot of wine.

TENSE: Past perfect indicates drinking precedes entering.

(2) Max entered the room. Mary was seated behind the desk.

ASPECT: State of ‘being seated’ overlaps with ‘entering’.

(3) He had borrowed some shirts from local villagers after his backpack went down.

TEMPORAL MODIFIER: Going down precedes borrowing, based on temporal adverbial after

(4) Iraq was defeated during the Gulf War. In ancient times it was the cradle of civilization.

TIMEX: Being the cradle precedes being defeated, based on explicit time expression.

(5) Max stood up. John greeted him.

NARR_CONVENTION: Narrative convention applies, with ‘standing up’ preceding ‘greeting’

(6) Max fell. John pushed him.

DISCOURSE_REL: Narrative convention overridden, based on Explanation relation

(7) A drunken man died in the central Philippines when he put a firecracker under his armpit.

DISCOURSE_REL: dying after putting, with temporal modifier used to instantiate Explanation relation

(8) U.N. Secretary- General Boutros Boutros-Ghali Sunday opened a meeting of .... Boutros-Ghali arrived in Nairobi from South Africa, accompanied by Michel...

WORLD KNOWLEDGE: arrival at the place of a meeting precedes opening a meeting

what s needed for computing chronologies
What’s Needed for Computing Chronologies?

Representation of tense and aspect

Representation of events and time

Linking of events and time

Result: a temporal constraint network

Here, both events and times are represented as pairs of points (nodes)

Ordering relations (edges) are <, =







Yesterday, Holly was running ….














[Verhagen 2004]

timeml annotation
TimeML Annotation
  • TimeML is a proposed metadata standard for markup of events and their temporal anchoring and ordering
  • Consists of EVENT tags, TIMEX3 tags, and LINK tags
    • EVENTS are grouped into classes and have tense and aspect features
    • LINKS include overt and covert links
      • Can be within or across sentences
how timeml differs from previous markups
How TimeML Differs from Previous Markups
  • Extends TIMEX2 annotation to TIMEX3
    • Temporal Functions: three years ago
    • Anchors to events and other temporal expressions: three years after the Gulf War
    • Addresses problem with Granularity/Periodicity: three days every month
    • Inserts start/end points for Durations: two weeks from June 7
  • Identifies signals determining interpretation of temporal expressions;
    • Temporal Prepositions:for, during, on, at;
    • Temporal Connectives: before, after, while.
  • Identifies event expressions;
    • tensed verbs; has left, was captured, will resign;
    • stative adjectives; sunken, stalled, on board;
    • event nominals; merger, Military Operation, Gulf War;
  • Creates dependencies between events and times:
    • Anchoring; John left on Monday.
    • Orderings; The party happened after graduation.
    • Embedding; John said Mary left.
  • TLINK or Temporal Link represents the temporal relationship holding between events or between an event and a time, and establishes a link between the involved entities, making explicit if they are:
  • Simultaneous (happening at the same time)
  • Identical: (referring to the same event)
  • John drove to Boston. During his drive he ate a donut.
  • One before the other:
    • The police looked into the slayings of 14 women.In six of the cases suspects have already been arrested.
  • One immediately before the other:
  • All passengers died when the plane crashed into the mountain.
  • One including the other:
  • John arrived in Boston last Thursday.
  • One holding during the duration of the other:
  • One being the beginning of the other:
  • John was in the gym between 6:00 p.m. and 7:00 p.m.
  • One being the ending of the other:
  • John was in the gym between 6:00 p.m. and 7:00 p.m.

SLINK or Subordination Link is used for contexts introducing relations between two events, or an event and a signal, of the following sort:

Modal: Relation introduced mostly by modal verbs (should, could, would, etc.) and events that introduce a reference to a possible world --mainly I_STATEs:

John should have bought some wine.

Mary wanted John to buy some wine.

Factive: Certain verbs introduce an entailment (or presupposition) of the argument's veracity. They include forget in the tensed complement, regret, manage:

John forgot that he was in Boston last year.

Mary regrets that she didn't marry John.

Counterfactive: The event introduces a presupposition about the non-veracity of its argument: forget (to), unable to (in past tense), prevent, cancel, avoid, decline, etc.

John forgot to buy some wine.

John prevented the divorce.

Evidential: Evidential relations are introduced by REPORTING or PERCEPTION:

John said he bought some wine.

Mary saw John carrying only beer.

Negative evidential: Introduced by REPORTING (and PERCEPTION?) events conveying negative polarity:

John denied he bought only beer.

Negative: Introduced only by negative particles (not, nor, neither, etc.), which will be marked as SIGNALs, with respect to the events they are modifying:

John didn't forget to buy some wine.

John did not want to marry Mary.

role of the machine in human annotation
Role of the machine in human annotation
  • In cases of dense annotation (events, pos tags, word-sense tags, etc.), it can be too tedious for a human to annotate everything
  • In such cases, it’s helpful to have a computer program pre-annotate the data that the human then corrects
  • The machine can also interact to flag invalid entries
  • The machine can also provide visualization
  • The machine can also augment the annotation with information that can be inferred
automatic timex2 tagging
Automatic TIMEX2 tagging
timeml annotation issues

Weaknesses in guidelines

Links between subordinate clause and main clause of same/diff sentence

Difficulties in annotating states

Granularity of temporal relations (72% agreement on temporal relations on common links)

Density of links. Number of links is quadratic in the number of events, but less than half the eventualities are linked.

So, inter-annotator agreement on links likely to be low.


Adding more annotation conventions

Lightening the annotation.

Expanding annotation using temporal reasoning.

Using heavily mixed-initiative approach

Providing user with visualization tools during annotation.

Note: such problems are characteristic of semantic and discourse-level annotations!

TimeML Annotation Issues
timebank browser and timeml tools
TimeBank Browser and TimeML tools
strategy for automatically inferring linguistic information
Strategy for Automatically Inferring Linguistic Information
  • Develop a corpus of TimeML annotated documents
    • TimeML represents temporal adverbials, tense, grammatical aspect, temporal relations
    • Takes into account subordination and (to an extent) vagueness
    • Work on metric constraints for durations of states is ongoing (Hobbs)
  • Develop initial computer taggers to tag Events, Times, and Links in the corpus
  • Correct the corpus using a human
  • Ensure that the annotations can be reproduced accurately
    • Inter-annotator reliability
  • Use the corpus to train improved computer taggers
at the florist s mini story
At the Florist’s (mini-story)
  • a. John went into the florist shop.
  • b. He had promised Mary some flowers.
  • c. She said she wouldn’t forgive him if he forgot.
  • d. So he picked out three red roses.
  • From (Webber 1988)
at the florist s a rhetorical structure theory account
Assumes abstract nodes which are Rhetorical Relations

Rhetorical relation annotations are not easily reproduced

question of inter-annotator reliability


Explanation Ed

Ea Elaboration


Eb Ec

At the Florist’s: A Rhetorical Structure Theory account
temporal relations as surrogates for rhetorical relations
When E1 is left-sibling of E2 and E1 < E2, then typically, Narration(E1, E2)

When E1 is right-sibling of E2 and E1 < E2, then typically Explanation(E2, E1)

When E2 is a child node of E1, then typically Elaboration(E1, E2)

Temporal Relations as Surrogates for Rhetorical Relations

a. John went into the florist shop.

b. He had promised Mary some flowers.

c. She said she wouldn’t forgive him if he forgot.

d. So he picked out three red roses.




constraints: {Eb < Ec, Ec < Ea, Ea < Ed}

temporal discourse model annotation conventions
Temporal Discourse Model Annotation Conventions
  • Each tree is rooted in an abstract node.
  • In the absence of any temporal adverbials or discourse markers, a tense shift will license the creation of an abstract node, with the tense shifted event being the leftmost daughter of the abstract node. The abstract node will then be inserted as the child of the immediately preceding text node.
  • In the absence of temporal adverbials and discourse markers, a stative event will always be placed as a child of the immediately preceding text event when the latter is non-stative, and as a sibling of the previous event when the latter isstative(as in a scene-setting fragment of discourse).
representing states
Approach: Minimality

A tensed stative predicate is represented as a node in the tree (progressives are treated as stative).

John walked home. He was feeling great.

We represent the state of feeling great as being minimally a part of the event of walking, without committing to whether it extends before or after the event

A constraint is added to C indicating that this inclusion is minimal.

Problem: Incompleteness

Max entered the room. He was wearing a black shirt

The system will not know whether the shirt was worn after he entered the room.

Representing States
tdms and drt
TDMs and DRT

EaEbEcxyzt1t2t3 [

enter(Ea, x, theWhiteHart) & man (x) & PROG(wear(Eb, x, y) & black-jacket(y) &serve(Ec, Bill, x, z) & beer(z) & t1 < n & Ea t1 & t2 < n & Eb o t2 & Eb Ea & t3 < n & Ec t3 & Ea < Ec]

what s needed for computing tdms
What’s Needed for Computing TDMs?
  • A Corpus of TDMs, annotated with high inter-annotator reliability
  • ‘Syntactic’ parsers for TDMs, trained on the corpus
  • There are lots of computational tools for manual and automatic annotation of linguistic data and exploration of linguistic hypotheses
  • The automatic tools aren’t perfect, but neither are humans!
  • An annotation scheme must be tested using guidelines and inter-annotator reliability
  • Annotations must be prepared and used within standard XML-based frameworks
  • There are many costs and tradeoffs in corpus preparation
  • The yields can considerably speed up the pace of linguistic research
desiderata for indian language work
Desiderata for Indian Language Work
  • The data needs to be encoded using standard character encoding schemes – UNICODE, or else ISCII
  • Annotation needs to follow the best-practices methodology, including proof of replicability, and XML representation
  • Experience has shown that linguists and computer scientists can work in synergy on this
  • Once corpora are prepared according to these guidelines, automatic tools can be developed in India and abroad and used to improve linguistic processing of Indian languages
    • Morphological analyzers, stemmers, etc.
    • Part-of-speech taggers
    • Syntactic Parsers
    • Word-Sense Disambiguators
    • Temporal Taggers
    • Information Extraction Systems
    • Text Summarizers
    • Statistical MT Systems
    • etc.
free resources contact me
Free Resources (contact me)
  • TIMEX2 corpora and tools: (English, Korean, Spanish)
  • TimeML and annotation tools:
  • AQUAINT corpus, and TimeML software: watch this space
  • PRONTO and iprolink corpora, guidelines, tagsets
  • (see my web site)

Thank You!

the changing environment
The Changing Environment
  • If statistical rules induced from examples perform just as well as rules derived from intuition, then this suggests that probabilistic statistical linguistic rules might help explain or model human linguistic behavior.
  • It also suggests that humans might learn from experience by means of induction using statistical regularities.
  • For many years, corpus linguistic research rarely examined statistics above the level of words, due to the lack of availability of broad-coverage parsers and statistical models that could handle syntax and other levels of ‘hidden structure’ (Manning 2003).
  • The present climate with plenty of tools and statistical models, should allow corpus linguistics to extend its descriptive and explanatory scope dramatically.
ngrams details
Ngrams Details
  • Consider a sequence of words W1…Wn, “I saw a rabbit”.
  • What’s P(W1…Wn)? Note that we can’t find sequences of length n, and count them - there won’t be enough data.
  • Chain Rule of probability:

P(W1, .. ,Wn ) =

P(W1)P(W2|W1) P(W3|W1,W2)..P(Wn|W1,W2, ..,Wn-1 )

    • But you still have the problem of lacking enough data
  • Bigram model
    • Approximates P(Wn|W1…Wn-1) by P(Wn|Wn-1)
    • Assumes the probability of a word depends just on the previous word. This means, that you don’t have to look back more than one word.
    • P(I saw a rabbit) = P(I|<s>)*P(saw|I)*P(a|saw)*P(rabbit|a)
    • More generally: P(W1….Wn) i=1, n P(Wi| Wi-1)
  • A trigram model, would look 2 words back into the past
    • P(I saw a rabbit) =P(saw|<s> I)*P(a| I saw)*P(rabbit|saw a)
pos tagging based on n grams
POS Tagging Based on N-grams
  • Problem: Find C which maximizes P(W | C) * P(C)
  • Here W=W1..Wn and C=C1..Cn (these were sequences, remember?)

P(W1, .. ,Wn ) =

P(W1)P(W2|W1) P(W3|W1,W2)..P(Wn|W1,W2, ..,Wn-1 )

    • Using the bigram model, we get:

P(W1….Wn | C1….Cn) i=1, n P(Wi| Ci)

P(C1….Cn) i=1, n P(Ci| Ci-1)

  • So, we want to find the value of C1..Cn which maximizes:

i=1, n P(Wi| Ci) * P(Ci| Ci-1)



probs, estimated

from training data

lexical generation

probabilities, estimated

from training data

problems in event anchoring
Problems in Event Anchoring
  • States
    • John walked home. He was feeling great.
      • How long does “feeling great” last?
        • => We need a “minimal” duration for states
    • a. Mary entered the President’s Office.b. A copy of the budget was on the president’s desk. c. The president’s financial advisor stood beside it. d. The president sat regarding both admiringly. e. The advisor spoke. (Dowty 1986)
      • Was the budget on the desk before she entered the office?
        • => “perceived scene” presents an imperfective view of states, not indicating their true onsets
  • Vagueness

The attack lasted 2-3 weeks.

Recently, Holly turned 16.

Next summer, Holly may run

Three days later, David pushed her

    • => temporal reasoning has to deal with vagueness
problems in event anchoring contd
Problems in Event Anchoring (contd)
  • Vagueness (contd)
    • John hurried to Mary’s house after work. But Mary had already left for dinner.
    • => we need to track ‘reference time’ and decide when reference times coincide
  • Modality
    • John should have brought some wine.
      • Did he bring wine? No.
    • John prevented the divorce.
      • Did the divorce happen? No.
      • => we need to know about subordination
  • Implicit Information

Yesterday, Holly fell. (implicit “on”)

Holly fell. David pushed her. (implicit “because”)

      • => we need discourse modeling