exploiting background knowledge for relation extraction

Exploiting Background Knowledgefor Relation Extraction

Yee Seng Chan and Dan Roth

University of Illinois at Urbana-Champaign

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Relation Extraction

Relation extraction (RE) “David Cone, a Kansas City native, was originally signed by the

Royals and broke into the majors with the team”

Supervised RE Train on sentences annotated with entity mentions and

predefined target relations Common features: BOW, POS tags, syntactic/dependency

parses, kernel functions based on structured representations of the sentence

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Background Knowledge

Features employed are usually restricted to being defined on the various representations of the target sentences

Humans rely on background knowledge to recognize relations

Overall aim of this work Propose methods of using knowledge or resources that exists

beyond the sentence Wikipedia, word clusters, hierarchy of relations, entity type

constraints, coreference As additional features, or under the Constraint Conditional Model

(CCM) framework with Integer Linear Programming (ILP)

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DavidCone,aKansasCitynative,wasoriginallysignedbytheRoyalsandbrokeintothemajorswiththeteam

Using Background Knowledge

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Using Background KnowledgeDavid Brian Cone (born January 2, 1963) is a former Major League Baseball pitcher. He compiled an 8–3 postseason record over 21 postseason starts and was a part of five World Series championship teams (1992 with the Toronto Blue Jays and 1996, 1998, 1999 & 2000 with the New York Yankees). He had a career postseason ERA of 3.80. He is the subject of the book A Pitcher's Story: Innings With David Cone by Roger Angell. Fans of David are known as "Cone-Heads."Cone lives in Stamford, Connecticut, and is formerly a color commentator for the Yankees on the YES Network.[1]

Contents[hide]1 Early years2 Kansas City Royals3 New York Mets

Partly because of the resulting lack of leadership, after the 1994 season the Royals decided to reduce payroll by trading pitcher David Cone and outfielder Brian McRae, then continued their salary dump in the 1995 season. In fact, the team payroll, which was always among the league's highest, was sliced in half from $40.5 million in 1994 (fourth-highest in the major leagues) to $18.5 million in 1996 (second-lowest in the major leagues)

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fine-grained

Employment:Staff 0.20

Employment:Executive 0.15

Personal:Family 0.10

Personal:Business 0.10

Affiliation:Citizen 0.20

Affiliation:Based-in 0.25

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fine-grained coarse-grained

Employment:Staff 0.200.35 Employment


Personal:Family 0.100.40 Personal


Affiliation:Citizen 0.200.25 Affiliation


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12










0.55

Basic Relation Extraction (RE) System

Our basicRE system Given a sentence “... m1 ... m2 ...”, predict whether any

predefined relation holds Asymmetric relations, e.g. m1:r:m2 vs m2:r:m1

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Our basicRE system Given a sentence “... m1 ... m2 ...”, predict whether any

predefined relation holds Asymmetric relations, e.g. m1:r:m2 vs m2:r:m1

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Most of the features based on the work in (Zhou et al., 2005)

Lexical: hw, BOW, bigrams, ... Collocations: words to the left/right of the mentions, ... Structural: m1-in-m2, #mentions between m1,m2, ...

Entity typing: m1,m2 entity-type, ...

Dependency: dep-path between m1,m2, ...

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Knowledge Sources

As additional features Wikipedia Word clusters

As constraints Hierarchy of relations Entity type constraints Coreference

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Knowledge1: Wikipedia1

(as additional feature)

We use a Wikifier system (Ratinov et al., 2010) which performs context-sensitive mapping of mentions to Wikipedia pages

Introduce a new feature based on:

introduce a new feature by combining the above with the coarse-grained entity types of mi,mj

otherwise ,0

)(or )( if ,1),(1

imjmji

mAmAmmw ji

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mi mj

r ?

Knowledge1: Wikipedia2

(as additional feature)

Given mi,mj, we use a Parent-Child system (Do and Roth, 2010) to predict whether they have a parent-child relation

Introduce a new feature based on:

combine the above with the coarse-grained entity types of mi,mj

otherwise ,0

),( if ,1),(2

jiji

mmchild-parentmmw

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mi mj

parent-child?

Knowledge2: Word Class Information(as additional feature)

Supervised systems face an issue of data sparseness (of lexical features)

Use class information of words to support generalization better: instantiated as word clusters in our work Automatically generated from unlabeled texts using algorithm of

(Brown et al., 1992)

apple pear Apple IBM

0 1 0 1

0 1

bought run of in

0 1 0 1

0 1

0 1

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Knowledge2: Word Class Information




apple pear Apple

0 1 0 1

0 1

bought run of in

0 1 0 1

0 1

0 1

20

IBMIBM





apple pear Apple

0 1 0 1

0 1

bought run of in

0 1 0 1

0 1

0 1

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IBMIBM011011


All lexical features consisting of single words will be duplicated with its corresponding bit-string representation

apple pear Apple IBM

0 1 0 1

0 1

bought run of in

0 1 0 1

0 1

0 1

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00 01 10 11

Knowledge Sources

As additional features Wikipedia Word clusters

As constraints Hierarchy of relations Entity type constraints Coreference

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weight vector for“local” models collection of

classifiers

Constraint Conditional Models (CCMs)(Roth and Yih, 2007; Chang et al., 2008)


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weight vector for“local” models collection of

classifiers

penalty for violatingthe constraint

how far y is from a “legal” assignment


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•Wikipedia•word clusters

•hierarchy of relations•entity type constraints•coreference


Goal of CCM: when you want to predict multiple variables, and you want to exploit the fact that they are related Encode knowledge as constraints to exploit interaction between

the multiple predictions You impose constraints on the predictions of your various models.

This is a global inference problem

We learn separate models and then perform joint global inference to arrive at final predictions

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Constraint Conditional Models (CCMs)








Key steps Write down a linear objective function Write down constraints as linear inequalities Solve using integer linear programming (ILP) packages

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Knowledge3: Relations between our target relations

......

personal

......

employment

family biz executivestaff

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Knowledge3: Hierarchy of Relations

......

personal

......

employment


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coarse-grainedclassifier

fine-grainedclassifier


......

personal

......

employment


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mi mj

coarse-grained?

fine-grained?


......

personal

......

employment


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......

personal

......

employment


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......

personal

......

employment


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......

personal

......

employment


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......

personal

......

employment


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Write down a linear objective function

R LR L R rf

rfRRR rc

rcRR

RfRc

yrfpxrcp ,, )()(max

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coarse-grainedprediction probabilities

fine-grainedprediction probabilities


Write down a linear objective function

R LR L R rf

rfRRR rc

rcRR

RfRc

yrfpxrcp ,, )()(max

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coarse-grainedprediction probabilities

fine-grainedprediction probabilities

coarse-grainedindicatorvariable

fine-grainedindicatorvariable

indicator variable == relation assignment


Write down constraints If a relation R is assigned a coarse-grained label rc, then we must

also assign to R a fine-grained relation rf which is a child of rc.

(Capturing the inverse relationship) If we assign rf to R, then we must also assign to R the parent of rf, which is a corresponding coarse-grained label

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nrfRrfRrfRrcR yyyx ,,,, 21

)(,, rfparentRrfR xy

Knowledge4: Entity Type Constraints(Roth and Yih, 2004, 2007)

Entity types are useful for constraining the possible labels that a relation R can assume

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mi mj

Employment:Staff

Employment:Executive

Personal:Family

Personal:Business

Affiliation:Citizen

Affiliation:Based-in

Entity types are useful for constraining the possible labels that a relation R can assume

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Employment:Staff


Personal:Family

Personal:Business

Affiliation:Citizen


per org

per org

per

per per

per

per

org

gpe

gpe

per per

mi mj


We gather information on entity type constraints from ACE-2004 documentation and impose them on the coarse-grained relations By improving the coarse-grained predictions and combining with the

hierarchical constraints defined earlier, the improvements would propagate to the fine-grained predications

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Employment:Staff


Personal:Family

Personal:Business

Affiliation:Citizen


per org

per org

per

per per

per

per

org

gpe

gpe

per per

mi mj


Knowledge5: Coreference

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mi mj

Employment:Staff


Personal:Family

Personal:Business

Affiliation:Citizen


Knowledge5: Coreference

In this work, we assume that we are given the coreference information, which is available from the ACE annotation.

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mi mj

Employment:Staff


Personal:Family

Personal:Business

Affiliation:Citizen


null

Experiments

Used the ACE-2004 dataset for our experiments Relations do not cross sentence boundaries We model the argument order (of the mentions)

m1:r:m2 vs m2:r:m1

Allow null label prediction when mentions are not related

Classifiers regularized averaged perceptrons implemented within the SNoW

(Carlson et al., 1999) Followed prior work (Jiang and Zhai, 2007) and performed 5-fold

cross validation

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Performance of the Basic RE System

Build a BasicRE system using only the basic features Compare against the state-of-the-art feature-based RE

system of Jiang and Zhai (2007) The authors performed their evaluation using undirected coarse-

grained relations (7 relation labels + 1 null label) Evaluation on nwire and bnews corpora of ACE-2004 Performance (F1%)

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Jiang and Zhai (2007) BasicRE

71.5% 71.2%

Experimental Settings

ACE-2004: 7 (coarse) and 23 (fine) grained relations Trained two classifiers: coarse-grained (15 relation labels) fine-grained (47 relation labels)

Focus on evaluation of fine-grained relations Use the nwire corpus for our experiments Two of our knowledge sources (Wiki system, word clusters) assume

inputs of mixed-case text bnews corpus in lower-cased text 28,943 relation instances with 2,226 (non-null)

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Evaluation Settings

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Prior work Our workTrain-test data splits at mention level

Train-test data splits at document level

Evaluation at mention level

Evaluation at entity level

more realistic

Experimental Settings

Evaluate our performance at the entity level Prior work calculated RE performance at the level of mentions ACE annotators rarely duplicate a relation link for coreferent

mentions:

Given a pair of entities, we establish the set of relation types existing between them, based on their mention annotations

r

... mi ... mj ... mk ...

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null?

Experiment Results (F1%): fine-grained relations

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All nwire 10% of nwire

BasicRE 50.5% 31.0%

Experiment Results (F1%): fine-grained relations

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F1% improvement from using each knowledge source

All nwire 10% of nwire

BasicRE 50.5% 31.0%

Related Work

Ji et al. (2005), Zhou et al. (2005,2008), Jiang (2009)

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Conclusion

We proposed a broad range of methods to inject background knowledge into a RE system

Some methods (e.g. exploiting the relation hierarchy) are general in nature

To combine the various relation predictions, we perform global inference within an ILP framework This allows for easy injection of knowledge as constraints Ensures globally coherent models and predictions

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exploiting background knowledge for relation extraction

Documents

background knowledgefeatures

emplo background knowledge0

cone lives

trading pitcher david

major leagues

leagues highest

e relation extraction

new york yankees