information extraction from the world wide web discriminative finite state models, feature induction...
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Information Extractionfrom the World Wide Web
Discriminative Finite State Models, Feature Induction & Scoped Learning
Andrew McCallumUniversity of Massachusetts, Amherst
An HR office
Jobs, but not HR jobs
Jobs, but not HR jobs
Extracting Job Openings from the Web
foodscience.com-Job2
JobTitle: Ice Cream Guru
Employer: foodscience.com
JobCategory: Travel/Hospitality
JobFunction: Food Services
JobLocation: Upper Midwest
Contact Phone: 800-488-2611
DateExtracted: January 8, 2001
Source: www.foodscience.com/jobs_midwest.html
OtherCompanyJobs: foodscience.com-Job1
This took place in ‘99
Not in Maryland
Courses from all over the world
Why prefer “knowledge base search” over “page search”
• Targeted, restricted universe of hits– Don’t show resumes when I’m looking for job openings.
• Specialized queries– Topic-specific
– Multi-dimensional
– Based on information spread on multiple pages.
• Get correct granularity– Site, page, paragraph
• Specialized display– Super-targeted hit summarization in terms of DB slot values
• Ability to support sophisticated data mining
What is “Information Extraction”
Filling slots in a database from sub-segments of text.As a task:
October 14, 2002, 4:00 a.m. PT
For years, Microsoft Corporation CEO Bill Gates railed against the economic philosophy of open-source software with Orwellian fervor, denouncing its communal licensing as a "cancer" that stifled technological innovation.
Today, Microsoft claims to "love" the open-source concept, by which software code is made public to encourage improvement and development by outside programmers. Gates himself says Microsoft will gladly disclose its crown jewels--the coveted code behind the Windows operating system--to select customers.
"We can be open source. We love the concept of shared source," said Bill Veghte, a Microsoft VP. "That's a super-important shift for us in terms of code access.“
Richard Stallman, founder of the Free Software Foundation, countered saying…
NAME TITLE ORGANIZATION
What is “Information Extraction”
Filling slots in a database from sub-segments of text.As a task:
October 14, 2002, 4:00 a.m. PT
For years, Microsoft Corporation CEO Bill Gates railed against the economic philosophy of open-source software with Orwellian fervor, denouncing its communal licensing as a "cancer" that stifled technological innovation.
Today, Microsoft claims to "love" the open-source concept, by which software code is made public to encourage improvement and development by outside programmers. Gates himself says Microsoft will gladly disclose its crown jewels--the coveted code behind the Windows operating system--to select customers.
"We can be open source. We love the concept of shared source," said Bill Veghte, a Microsoft VP. "That's a super-important shift for us in terms of code access.“
Richard Stallman, founder of the Free Software Foundation, countered saying…
NAME TITLE ORGANIZATIONBill Gates CEO MicrosoftBill Veghte VP MicrosoftRichard Stallman founder Free Soft..
IE
What is “Information Extraction”
Information Extraction = segmentation + classification + clustering + association
As a familyof techniques:
October 14, 2002, 4:00 a.m. PT
For years, Microsoft Corporation CEO Bill Gates railed against the economic philosophy of open-source software with Orwellian fervor, denouncing its communal licensing as a "cancer" that stifled technological innovation.
Today, Microsoft claims to "love" the open-source concept, by which software code is made public to encourage improvement and development by outside programmers. Gates himself says Microsoft will gladly disclose its crown jewels--the coveted code behind the Windows operating system--to select customers.
"We can be open source. We love the concept of shared source," said Bill Veghte, a Microsoft VP. "That's a super-important shift for us in terms of code access.“
Richard Stallman, founder of the Free Software Foundation, countered saying…
Microsoft CorporationCEOBill GatesMicrosoftGatesMicrosoftBill VeghteMicrosoftVPRichard StallmanfounderFree Software Foundation
What is “Information Extraction”
Information Extraction = segmentation + classification + association + clustering
As a familyof techniques:
October 14, 2002, 4:00 a.m. PT
For years, Microsoft Corporation CEO Bill Gates railed against the economic philosophy of open-source software with Orwellian fervor, denouncing its communal licensing as a "cancer" that stifled technological innovation.
Today, Microsoft claims to "love" the open-source concept, by which software code is made public to encourage improvement and development by outside programmers. Gates himself says Microsoft will gladly disclose its crown jewels--the coveted code behind the Windows operating system--to select customers.
"We can be open source. We love the concept of shared source," said Bill Veghte, a Microsoft VP. "That's a super-important shift for us in terms of code access.“
Richard Stallman, founder of the Free Software Foundation, countered saying…
Microsoft CorporationCEOBill GatesMicrosoftGatesMicrosoftBill VeghteMicrosoftVPRichard StallmanfounderFree Software Foundation
What is “Information Extraction”
Information Extraction = segmentation + classification + association + clustering
As a familyof techniques:
October 14, 2002, 4:00 a.m. PT
For years, Microsoft Corporation CEO Bill Gates railed against the economic philosophy of open-source software with Orwellian fervor, denouncing its communal licensing as a "cancer" that stifled technological innovation.
Today, Microsoft claims to "love" the open-source concept, by which software code is made public to encourage improvement and development by outside programmers. Gates himself says Microsoft will gladly disclose its crown jewels--the coveted code behind the Windows operating system--to select customers.
"We can be open source. We love the concept of shared source," said Bill Veghte, a Microsoft VP. "That's a super-important shift for us in terms of code access.“
Richard Stallman, founder of the Free Software Foundation, countered saying…
Microsoft CorporationCEOBill GatesMicrosoftGatesMicrosoftBill VeghteMicrosoftVPRichard StallmanfounderFree Software Foundation
What is “Information Extraction”
Information Extraction = segmentation + classification + association + clustering
As a familyof techniques:
October 14, 2002, 4:00 a.m. PT
For years, Microsoft Corporation CEO Bill Gates railed against the economic philosophy of open-source software with Orwellian fervor, denouncing its communal licensing as a "cancer" that stifled technological innovation.
Today, Microsoft claims to "love" the open-source concept, by which software code is made public to encourage improvement and development by outside programmers. Gates himself says Microsoft will gladly disclose its crown jewels--the coveted code behind the Windows operating system--to select customers.
"We can be open source. We love the concept of shared source," said Bill Veghte, a Microsoft VP. "That's a super-important shift for us in terms of code access.“
Richard Stallman, founder of the Free Software Foundation, countered saying…
Microsoft CorporationCEOBill GatesMicrosoftGatesMicrosoftBill VeghteMicrosoftVPRichard StallmanfounderFree Software Foundation N
AME
TITLE ORGANIZATION
Bill Gates
CEO
Microsoft
Bill Veghte
VP
Microsoft
Richard Stallman
founder
Free Soft..
*
*
*
*
IE in Context
Create ontology
SegmentClassifyAssociateCluster
Load DB
Spider
Query,Search
Data mine
IE
Documentcollection
Database
Filter by relevance
Label training data
Train extraction models
Hidden Markov Models
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Finite state model Graphical model
Parameters: for all states S={s1,s2,…} Start state probabilities: P(st) Transition probabilities: P(st|st-1) Observation (emission) probabilities: P(ot|st)Training: Maximize probability of training observations (w/ prior)
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HMMs are the standard sequence modeling tool in genomics, speech, NLP, …
...transitions
observations
o1 o2 o3 o4 o5 o6 o7 o8
Generates:
State sequenceObservation sequence
Usually a multinomial over atomic, fixed alphabet
IE with Hidden Markov Models
Yesterday Lawrence Saul spoke this example sentence.
Yesterday Lawrence Saul spoke this example sentence.
Person name: Lawrence Saul
Given a sequence of observations:
and a trained HMM:
Find the most likely state sequence: (Viterbi)
Any words said to be generated by the designated “person name”state extract as a person name:
),(maxarg osPs
HMM Example: “Nymble”
Other examples of shrinkage for HMMs in IE: [Freitag and McCallum ‘99]
Task: Named Entity Extraction
[Bikel, et al 1998], [BBN “IdentiFinder”]
Person
Org
Other
(Five other name classes)
start-of-sentence
end-of-sentence
Transitionprobabilities
Observationprobabilities
P(st | st-1, ot-1 ) P(ot | st , st-1 )
Back-off to: Back-off to:
P(st | st-1 )
P(st )
P(ot | st , ot-1 )
P(ot | st )
P(ot )
or
Regrets from Atomic View of Tokens
Would like richer representation of text: multiple overlapping features, whole chunks of text.
line, sentence, or paragraph features:– length– is centered in page– percent of non-alphabetics– white-space aligns with next line– containing sentence has two verbs– grammatically contains a question– contains links to “authoritative” pages– emissions that are uncountable– features at multiple levels of granularity
Example word features:– identity of word– is in all caps– ends in “-ski”– is part of a noun phrase– is in a list of city names– is under node X in WordNet or Cyc– is in bold font– is in hyperlink anchor– features of past & future– last person name was female– next two words are “and Associates”
Problems with Richer Representationand a Generative Model
• These arbitrary features are not independent:– Overlapping and long-distance dependences
– Multiple levels of granularity (words, characters)
– Multiple modalities (words, formatting, layout)
– Observations from past and future
• HMMs are generative models of the text:
• Generative models do not easily handle these non-independent features. Two choices:– Model the dependencies. Each state would have its own
Bayes Net. But we are already starved for training data!
– Ignore the dependencies. This causes “over-counting” of evidence (ala naïve Bayes). Big problem when combining evidence, as in Viterbi!
),( osP
Conditional Sequence Models
• We would prefer a conditional model:P(s|o) instead of P(s,o):– Can examine features, but not responsible for generating
them.
– Don’t have to explicitly model their dependencies.
– Don’t “waste modeling effort” trying to generate what we are given at test time anyway.
• This answers the challenge of integrating the ability to handle many arbitrary features with the full power of finite state automata.
Locally Normalized Conditional Sequence Model
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Generative (traditional HMM)
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...transitions
observations
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Conditional
...transitions
observations
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Standard belief propagation: forward-backward procedure.Viterbi and Baum-Welch follow naturally.
Maximum Entropy Markov Models [McCallum, Freitag & Pereira, 2000]MaxEnt POS Tagger [Ratnaparkhi, 1996]
SNoW-based Markov Model [Punyakanok & Roth, 2000]
Locally Normalized Conditional Sequence Model
St -1
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St+1
Ot +1
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Generative (traditional HMM)
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...transitions
observations
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Conditional
...transitions
entire observation sequence
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Standard belief propagation: forward-backward procedure.Viterbi and Baum-Welch follow naturally.
Maximum Entropy Markov Models [McCallum, Freitag & Pereira, 2000]MaxEnt POS Tagger [Ratnaparkhi, 1996]
SNoW-based Markov Model [Punyakanok & Roth, 2000]
Or, more generally:
...
Exponential Form for “Next State” Function
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Overall Recipe:- Labeled data is assigned to transitions.- Train each state’s exponential model by maximum likelihood (iterative scaling or conjugate gradient).
weight feature
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Black-box classifier
st-1
Feature Functions
:),,,( Example 1ttk sstof
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Yesterday Lawrence Saul spoke this example sentence.
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Exponential Form for “Next State” Function
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Overall Recipe:- Labeled data is assigned to transitions.- Train each state’s exponential model by maximum likelihood (iterative scaling or conjugate gradient).
weight feature
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Black-box classifier
st-1
Experimental Data
38 files belonging to 7 UseNet FAQs
Example:
<head> X-NNTP-Poster: NewsHound v1.33<head> Archive-name: acorn/faq/part2<head> Frequency: monthly<head><question> 2.6) What configuration of serial cable should I use?<answer><answer> Here follows a diagram of the necessary connection<answer> programs to work properly. They are as far as I know <answer> agreed upon by commercial comms software developers fo<answer><answer> Pins 1, 4, and 8 must be connected together inside<answer> is to avoid the well known serial port chip bugs. The
Procedure: For each FAQ, train on one file, test on other; average.
Features in Experiments
begins-with-number
begins-with-ordinal
begins-with-punctuation
begins-with-question-word
begins-with-subject
blank
contains-alphanum
contains-bracketed-number
contains-http
contains-non-space
contains-number
contains-pipe
contains-question-mark
contains-question-word
ends-with-question-mark
first-alpha-is-capitalized
indented
indented-1-to-4
indented-5-to-10
more-than-one-third-space
only-punctuation
prev-is-blank
prev-begins-with-ordinal
shorter-than-30
Models Tested
• ME-Stateless: A single maximum entropy classifier applied to each line independently.
• TokenHMM: A fully-connected HMM with four states, one for each of the line categories, each of which generates individual tokens (groups of alphanumeric characters and individual punctuation characters).
• FeatureHMM: Identical to TokenHMM, only the lines in a document are first converted to sequences of features.
• MEMM: The Maximum Entropy Markov Model described in this talk.
Results
Learner Segmentationprecision
Segmentationrecall
ME-Stateless 0.038 0.362
TokenHMM 0.276 0.140
FeatureHMM 0.413 0.529
MEMM 0.867 0.681
nn oooossss ,...,,..., 2121
HMM
MEMM
CRF
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(A special case of MEMMs and CRFs.)
Conditional Random Fields (CRFs)[Lafferty, McCallum, Pereira ‘2001]
From HMMs to MEMMs to CRFs
Conditional Random Fields (CRFs)
St St+1 St+2
O = Ot, Ot+1, Ot+2, Ot+3, Ot+4
St+3 St+4
Markov on s, conditional dependency on o.
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Hammersley-Clifford-Besag theorem stipulates that the CRFhas this form—an exponential function of the cliques in the graph.
Assuming that the dependency structure of the states is tree-shaped (linear chain is a trivial tree), inference can be done by dynamic programming in time O(|o| |S|)—just like HMMs.
[Lafferty, McCallum, Pereira ‘2001]
General CRFs vs. HMMs
• More general and expressive modeling technique
• Comparable computational efficiency
• Features may be arbitrary functions of any or all observations
• Parameters need not fully specify generation of observations; require less training data
• Easy to incorporate domain knowledge
• State means only “state of process”, vs“state of process” and “observational history I’m keeping”
Training CRFs
),,,(),(
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penalty smoothing parameterscurrent by assigned labels usingcount feature labelscorrect usingcount feature
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Methods:• iterative scaling (quite slow)• conjugate gradient (much faster)• conjugate gradient with preconditioning (super fast)• limited-memory quasi-Newton methods (also super fast)
Complexity comparable to standard Baum-Welch
[Sha & Pereira 2002]& [Malouf 2002]
Voted Perceptron Sequence Models
before as ),,,(),( where
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[Collins 2002]
Like CRFs with stochastic gradient ascent and a Viterbi approximation.
Avoids calculating the partition function (normalizer), Zo, but gradient ascent, not 2nd-order or conjugate gradient method.
Analogous tothe gradientfor this onetraining instance
MEMM & CRF Related Work• Maximum entropy for language tasks:
– Language modeling [Rosenfeld ‘94, Chen & Rosenfeld ‘99]– Part-of-speech tagging [Ratnaparkhi ‘98]– Segmentation [Beeferman, Berger & Lafferty ‘99]– Named entity recognition “MENE” [Borthwick, Grishman,…’98]
• HMMs for similar language tasks– Part of speech tagging [Kupiec ‘92]– Named entity recognition [Bikel et al ‘99]– Other Information Extraction [Leek ‘97], [Freitag & McCallum ‘99]
• Serial Generative/Discriminative Approaches– Speech recognition [Schwartz & Austin ‘93]– Reranking Parses [Collins, ‘00]
• Other conditional Markov models– Non-probabilistic local decision models [Brill ‘95], [Roth ‘98]– Gradient-descent on state path [LeCun et al ‘98]– Markov Processes on Curves (MPCs) [Saul & Rahim ‘99]– Voted Perceptron-trained FSMs [Collins ’02]
Part-of-speech Tagging
The asbestos fiber , crocidolite, is unusually resilient once
it enters the lungs , with even brief exposures to it causing
symptoms that show up decades later , researchers said .
DT NN NN , NN , VBZ RB JJ IN
PRP VBZ DT NNS , IN RB JJ NNS TO PRP VBG
NNS WDT VBP RP NNS JJ , NNS VBD .
45 tags, 1M words training data, Penn Treebank
Error oov error error err oov error err
HMM 5.69% 45.99%
CRF 5.55% 48.05% 4.27% -24% 23.76% -50%
Using spelling features*
* use words, plus overlapping features: capitalized, begins with #, contains hyphen, ends in -ing, -ogy, -ed, -s, -ly, -ion, -tion, -ity, -ies.
[Pereira 2001]
Chinese Word Segmentation[McCallum & Feng 2003]
~100k words data, Penn Chinese Treebank
Lexicon features:
Adjective ending character digit characters provincesadverb ending character foreign name chars punctuation charsbuilding words function words Roman alphabeticsChinese number characters job title Roman digitsChinese period locations stopwordscities and regions money surnamescountries negative characters symbol charactersdates organization indicator verb charsdepartment characters preposition characters wordlist (188k lexicon)
Chinese Word Segmentation Results[McCallum & Feng 2003]
Precision and recall of segments with perfect boundaries:
# training testing segmentationMethod sentences prec. recall F1
[Peng] ~5M 75.1 74.0 74.2[Ponte] ? 84.4 87.8 86.0[Teahan] ~40k ? ? 94.4[Xue] ~10k 95.2 95.1 95.2CRF 2805 97.3 97.8 97.5CRF 140 95.4 96.0 95.7CRF 56 93.9 95.0 94.4CRF+ 2805 99.6 99.7 99.6
Prev. world’s best error 50%
Person name Extraction[McCallum 2001]
Features in Experiment
Capitalized Xxxxx
Mixed Caps XxXxxx
All Caps XXXXX
Initial Cap X….
Contains Digit xxx5
All lowercase xxxx
Initial X
Punctuation .,:;!(), etc
Period .
Comma ,
Apostrophe ‘
Dash -
Preceded by HTML tag
Character n-gram classifier says string is a person name (80% accurate)
In stopword list(the, of, their, etc)
In honorific list(Mr, Mrs, Dr, Sen, etc)
In person suffix list(Jr, Sr, PhD, etc)
In name particle list (de, la, van, der, etc)
In Census lastname list;segmented by P(name)
In Census firstname list;segmented by P(name)
In locations lists(states, cities, countries)
In company name list(“J. C. Penny”)
In list of company suffixes(Inc, & Associates, Foundation)
Hand-built FSM person-name extractor says yes, (prec/recall ~ 30/95)
Conjunctions of all previous feature pairs, evaluated at the current time step.
Conjunctions of all previous feature pairs, evaluated at current step and one step ahead.
All previous features, evaluated two steps ahead.
All previous features, evaluated one step behind.
Total number of features = ~200k
Training and Testing
• Trained on 65469 words from 85 pages, 30 different companies’ web sites.
• Training takes 4 hours on a 1 GHz Pentium.• Training precision/recall is 96/96.
• Tested on different set of web pages with similar size characteristics.
• Testing precision is 0.92 - 0.95, recall is 0.89 - 0.91.
Feature Induction
WORD=“interest” & WORD@+1=“rates”
WORD=“put” & WORD@+1=“and” & WORD@+2=“call” (options)
WORD=“to” & POS@+1=VB
# features without conjunctions = ~90k# features with conjunctions = ~1 million
Feature Gain
)||~()||~(),(Gain fq qpDqpDf
Currentloss
Loss if feature fwere added andhad optimal weight,
Feature Induction Procedure
• Partially train model with current features• Find tokens significantly contributing to D(p||q).• “Cluster” these errors by different cells of the
confusion matrix.• For each cell
– Generate ~50k candidate new features– Measure the Gain of each– Add to the model the top N features
~
Feature Induction Discussion
• Decision trees partition the training data.• Boosting is like feature induction
– (Generate a new conjunction or tree & give it a weight)– but it typically adds just one feature for each round– and it doesn’t change the weight once set.
• [Della Piettra2 & Lafferty 97]– also add one feature at a time, and would be quite
inefficient for CRFs.
• Here we carefully select several approximations to their scheme.
Feature Induction Results (Preliminary)
Noun Phrase Segmentation
Method # features F1
[Sha & Pereira 2003] 3.8M 94.4Feature Induction 140K 94.4
Named Entity Extraction (in Spanish)
Method F1
With no conjunctions ~30With fixed conjunctions 51With induced conjunctions 65
(extra preliminary)
Person name Extraction
Local features, like formatting, exhibit regularity on a particular subset of the data (e.g. web site or document). Note that future data will probably not have the same regularities as the training data.
Global features, like word content, exhibit regularity over an entire data set. Traditional classifiers are generally trained on these kinds of features.
Local and Global Features
w
f
Scoped Learning Generative Model
1. For each of the D documents:a) Generate the multinomial formatting
feature parameters from p(|)
2. For each of the N words in the document:
a) Generate the nth category cn from
p(cn).
b) Generate the nth word (global feature)
from p(wn|cn,)
c) Generate the nth formatting feature
(local feature) from p(fn|cn,)
w f
c
N
D
Inference
Given a new web page, we would like to classify each wordresulting in c = {c1, c2,…, cn}
This is not feasible to compute because of the integral andsum in the denominator. We experimented with twoapproximations: - MAP point estimate of - Variational inference
MAP Point Estimate
If we approximate with a point estimate, , then the integral disappears and c decouples. We can then label each word with:
E-step:
M-step:
A natural point estimate is the posterior mode: a maximum likelihood estimate for the local parameters given the document in question:
^
Global Extractor: Correctly extracts 3 out of 9
Scoped Learning Extractor: Correctly extracts 8 out of 9
Coverage
Acc
ura
cy
Global Extractor: Precision = 46%, Recall = 75%
Scoped Learning Extractor: Precision = 58%, Recall = 75% Error = -22%
Discriminative Model
w f
c
N
D
When there are many non-independent formatting features, may prefer a non-generative model.
Use a point estimate of .
E-step computes p(c|w, f, ).
M-step sets to maximize conditional likelihood, p(c|f)—uses MaxEnt.
More Experimental Results
• 42,548 web pages from 330 web sites. Each page labeled as PRESS_RELEASE, OTHER.
• Locale: web site• Global features: words on page
– E.g. “immediate” “release” “products”
• Local features: Character 4-gram window slid across URL.– E.g. “prel”, “/pr/”, “pres”…
Global Extractor: Precision = 54%, Recall = 90%
Scoped Learning Extractor: Precision = 77%, Recall = 90% Error = -50%
Scoped Learning Related Work
• Co-training [Blum & Mitchell 1998]– Although it has no notion of scope, it also has an independence
assumption about two independent views of data.
• PRMs for classification [Taskar, Segal & Koller 2001]– Extends notion of multiple views to multiple kinds of relationships– This model can be cast as a PRM where each locale is a separate group
of nodes with separate parameters. Their inference corresponds our MAP estimate inference.
• Classification with Labeled & Unlabeled Data [Nigam et al, 1999, Joachims 1999, etc.]– Particularly transduction, in which the unlabeled set is the test set. – However, we model locales, represent a difference between local and
global features, and can use locales at training time to learn hyper-parameters over local features.
• Classification with Hyperlink Structure [Slattery 2001]– Adjusts a web page classifier using ILP and a hubs & authorities
algorithm.
Future Directions• Further work in feature selection and induction: automatically
choose the fk functions (efficiently).
• Factorial CRFs
• Tree-structured Markov random fields for hierarchical parsing.
• Induction of finite state structure.
• Combine CRFs and Scoped Learning.
• Data mine the results of information extraction, and integrate the data mining with extraction.
• Create a text extraction and mining system that can be assembled and trained to a new vertical application by non-technical users.
Papers on MEMMs, CRFs, Scoped Learning and more available at http://www.cs.umass.edu/~mccallum
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