Introduction to Information Extraction

Chia-Hui Chang

Dept. of Computer Science and Information Engineering, National

Central University, Taiwanchia@csie.ncu.edu.tw

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Problem Definition Information Extraction (IE) is to identify

relevant information from documents, pulling information from a variety of sources and aggregates it into a homogeneous form.

Input extractor structured output

The output template of the IE task Several fields (slots) Several instances of a field

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Difficulties of IE tasks depends on …

Text type From plain text to semi-structured Web

pages e.g. Wall Street Journal articles, or

email message, HTML documents. Domain

From financial news, or tourist information, to various language.

Scenario

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Various IE Tasks Free-text IE:

For MUC (Message Understanding Conference) E.g. terrorist activities, corporate joint

ventures

Semi-structured IE: E.g.: meta-search engines, shopping agents,

Bio-integration system

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Types of IE from MUC Named Entity recognition (NE)

Finds and classifies names, places, etc. Coreference Resolution (CO)

Identifies identity relations between entities in texts.

Template Element construction (TE) Adds descriptive information to NE results.

Scenario Template production (ST) Fits TE results into specified event scenarios.

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Named Entity Recognitionhttp://www.cs.nyu.edu/cs/faculty/grishman/NEtask20.book_3.html

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NE Recognition (Cont.) Spanish:

93% Japanese:

92% Chinese:

84.51%

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Coreference Resolution Coreference resolution (CO) involves

identifying identity relations between entities in texts.

For example, in

Alas, poor Yorick, I knew him well.

Tie “Yorick" with “him“. The Sheffield system scored 51% recall and

71% precision.

http://www.cs.nyu.edu/cs/faculty/grishman/COtask21.book_4.html

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Template Element Production Adds description with named entities Sheffield system scores 71%

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Scenario Template Extraction STs are the

prototypical outputs of IE systems

They tie together TE entities into event and relation descriptions.

Performance for Sheffield: 49%

http://www.cs.nyu.edu/cs/ faculty/grishman/ IEtask15.book_2.html

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Example The operational domains that user interests are centered

around are drug enforcement, money laundering, organized crime, terrorism, ….

1. Input: texts dealing with drug enforcement, money laundering, organized crime, terrorism, and legislation;

2. NE: recognizes entities in those texts and assigns them to one of a number of categories drawn from the set of entities of interest (person, company, . . . );

3. TE: associates certain types of descriptive information with these entities, e.g. the location of companies;

4. ST: identifies a set (relatively small to begin with) of events of interest by tying entities together into event relations.

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Example Text

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Output Example (NE, TE)

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Output (STs)

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Another IE Example Corporate Management Changes Purpose

which positions in which organizations are changing hands?

who is leaving a position and where the person is going to? who is appointed to a position and where the person is

coming from? the locations and types of the organizations involved in the

succession events; the names and titles of the persons involved in the

succession events

http://www.cs.umanitoba.ca/~lindek/ie-ex.htm

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Input TextPresident Clinton nominated John Rollwagen, the chairman

and CEO of Cray Research Inc., as the No. 2 Commerce Department official. Mr. Rollwagen said he wants to push the Clinton administration to aggressively confront U.S. trading partners such as Japan to open their markets, particularly for high-tech industries. In a letter sent throughout the Eagan, Minn.-based company on Friday, Mr. Rollwagen warned: "Whether we like it or not, our country is in an economic war; and we are at a key turning point in that war." ......

Cray said it has appointed John F. Carlson, its president and chief operating officer, to succeed him. ......

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Extraction ResultCorporate Management Database

Person Organization Position Transition

John Rollwagen Cray Research Inc. chairman out

John Rollwagen Cray Research Inc. CEO out

John F. Carlson Cray Research Inc. chairman in

John F. Carlson Cray Research Inc. CEO in

Organization Database

Name Location Alias Type

Cray Research Inc. Eagan, Minn. Cray COMPANY

Commerce Department GOVERNMENT

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MUC Data Set for

MET2 http://www.itl.nist.gov/iaui/894.02/related_projects/muc/met2/met2package.tar.gz

MUC3&4 http://www.itl.nist.gov/iaui/894.02/related_projects/muc/muc_data/muc34.tar.gz

MUC6&7 from LDC http://www.ldc.upenn.edu/ MUC-6:

http://www.cs.nyu.edu/cs/faculty/grishman/muc6.html MUC-7 http://www.itl.nist.gov/iaui/894.02/related_projects/muc/

proceedings/muc_7_toc.html

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Summary Evaluation

Precision= Recall=

Design Methodology for Text IE Natural Language Processing Machine Learning

# of correctly extracted fields# of extracted fields

# of correctly extracted fields# of fields to be extracted

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IE from Web pages

Output Template: k-tuple Multiple instances of a field Missing data

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Web data extraction

Various Web pages Multiple-record page extraction One-record (singular) page extraction

Multiple-record page extraction

One-record (singular) page extraction

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Applications Information integration

Meta Search Engines Shopping agents Travel agents

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Information Integration Systems

Unprocessed,Unintegrated

Details

Translation and Wrapping

Semantic Integration

Mediation

AbstractedInformation

Text,Images/Video,Spreadsheets

Hierarchical& NetworkDatabases

RelationalDatabases

Object &Knowledge

Bases

SQL ORBWrapper Wrapper

Mediator Mediator

Human & Computer Users

Heterogeneous Data Sources

InformationIntegrationService

Mediator

User Services:• Query• Monitor• Update Agent/Module

Coordination

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Web Wrappers What is a wrapper?

An extracting program to extract desired information from Web pages.Web pages → wrapper→ Structure Info.

Web wrappers wrap... “Query-able’’ or “Search-able’’ Web sites Web pages with large itemized lists

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Summary Evaluation

Precision= Recall=

Methodology for Web IE Programming package Machine Learning Pattern Mining

# of correctly extracted records# of extracted records

# of correctly extracted records# of records to be extracted

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Type III: News Group IE Example: Computer-Related Jobs

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Output Template

Between free-text IE and semi-structured IE [CaliffRapier 99]

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Wrapper Induction Systems

Wrapper induction (WI) or information extraction (IE) systems are software that are designed to generate wrappers.

Taxonomy of Web IE systems by Task domain

• free text vs semi-structured pages Automation degree

• supervised vs unsupervised Techniques applied

• Machine learning vs pattern mining

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Task Domain Document type Extraction level

Field-level, record-level, page-level Extraction target variation

Missing Attributes Multi-valued Attributes Multi-order attribute Permutations Nested Data Objects

Template variation Various Templates for an attribute Common Templates for various attributes

Untokenized Attributes

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Automation Degree

Page-fetching Support Annotation Requirement Output Support API Support

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Techniques Applied Scan passes Extraction rule types Learning algorithms Tokenization schemes Feature used

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Conclusion Define the IE problem Specify the input: training example

with annotation, or without annotation

Depict the extraction rule Use necessary background knowledge

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References *H. Cunningham, Information Extraction – a User

Guide, http://www.dcs.shef.ac.uk *MUC-6, http://www.cs.nyu.edu/cs/faculty/

grishman/muc6.html *I. Muslea,

Extraction Patterns for Information Extraction Tasks: A Survey, The AAAI-99 Workshop on Machine Learning for Information Extraction.

Califf, Relational Learning of Pattern-Matching Rule for Information Extraction, AAAI-99.