Text Retrieval and Mining # 11-1 Information Extraction

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1 Text Retrieval and Mining # 11-1 Information Extraction
Lecture by Young Hwan CHO, Ph. D.

2 Plan for Today Information Extraction Introduction to the IE problem
Wrappers Wrapper Induction Traditional NLP-based IE Pattern Learning Systems: Rapier Probabilistic sequence models: HMMs

3 What is Information Extraction?
the extraction or pulling out of pertinent information from large volumes of texts 어떠한 문서를 사용자가 읽어야 한다는 것을 알려주기보다는 사용자에게 필요한 부분의 정보의 조각을 추출하고, 추출된 정보와 원래의 문서간의 링크를 유지해서 사용자가 내용을 참조하도록 링크하는 것 이러한 정보는 신뢰성이 높고 자세하여야 하는데, 최근의 기술로는 아래와 같은 수준을 보인다. Items of Information Definitions Percentile Reliability Entities an object of interest such as a person or organization 90 Attributes a property of an entity such as its name, alias, descriptor, or type 80 Facts a relationship held between two or more entities 70 Events an activity or occurrence of interest such as a terrorist act or an airline crash 60

4 IE from the Web: The Big Picture

5 Information Extraction의 컴포넌트
Spider : 웹 페이지 수집 대상이 되는 웹페이지를 수집, 다음 페이지 URL 찾기 Wrapper : HTML 페이지 -> XML DB CGI 스타일의 페이지에서는 Wrapper 만으로도 충분히 역할을 할 수 있음 NLP Lib : 문장에서 정보 추출 Free Style의 HTML, 설명형태의 글, 뉴스 등에서 특정 Fact 수집 DB는 Text 보다 과거의 데이터를 담고 있음 Information Cooking Identification : 문서 스타일 판별 Segmentation : 문서의 구성요소 조각 나눔 Classification : 문서내의 entity 범주화, 문서 범주화 Clustering : 문서내의 entury 군집화, 문서 군집화 Association : 문서내의 정보를 DB의 Field로 매핑

6 Examples : Corpus Fletcher Maddox, former Dean of the UCSD Business School, announced the formation of La Jolla Genomatics together with his two sons. La Jolla Genomatics will release its product Geninfo in June Geninfo is a turnkey system to assist biotechnology researchers in keeping up with the voluminous literature in all aspects of their field. Dr. Maddox will be the firm's CEO. His son, Oliver, is the Chief Scientist and holds patents on many of the algorithms used in Geninfo. Oliver's brother, Ambrose, follows more in his father's footsteps and will be the CFO of L.J.G. headquartered in the Maddox family's hometown of La Jolla, CA.

7 Examples : Entity Persons: Organizations: Locations: Artifacts: Dates:
Fletcher Maddox UCSD Business School La Jolla Geninfo June 1999 Dr. Maddox La Jolla Genomatics CA Oliver L.J.G. Ambrose Maddox

8 Examples : Attributes Fletcher Maddox Maddox
former Dean of the UCSD Business School his father the firm's CEO PERSON Oliver His son Chief Scientist Ambrose Oliver's brother the CFO of L.J.G. UCSD Business School NAME: DESCRIPTOR: CATEGORY: ORGANIZATION La Jolla Genomatics L.J.G. ORGANIZATION Geninfo its product ARTIFACT La Jolla the Maddox family's hometown LOCATION CA NAME: DESCRIPTOR: CATEGORY:

9 Examples : Facts PERSON Employee_of ORGANIZATION
Fletcher Maddox Fletcher Maddox Oliver Ambrose Employee_of Employee_of Employee_of Employee_of UCSD Business School La Jolla Genomatics La Jolla Genomatics La Jolla Genomatics ARTIFACT Product_of Geninfo La Jolla Genomatics LOCATION Location_of La Jolla CA

10 Examples : Events 회사설립 이벤트 COMPANY: La Jolla Genomatics PRINCIPALS:
Fletcher Maddox Oliver Ambrose DATE: CAPITAL: 상품출시 이벤트 COMPANY: La Jolla Genomatics PRODUCT: Geninfo DATE: June 1999 COST:

11 Unstructured Data -> Strcutured/Semi-Structured Data
Task = Filling slots in a database from sub-segments of text Techniques = Segmentation + classification + clustering + association

12 Source Styles

13 Segmentation Extract metadata (e.g. author, title, date)
Identify sections (e.g. abstract) Extract keywords

14 Clustering + Classification
Document 내부에서 문서내의 Named Entity에 대해서 Entity Type을 판단 인명, 직책, 기관명, 날짜, 기관, 단위, 주소 제목, 나열형 문장, 설명형 문장 동일 데이터 형태가 나열된 경우에, 밝혀진 것과 동일한 패턴으로 나열된 데이터에 대해서 동일한 filed로 인정 여러 Document로부터 추출된 정보의 신뢰도를 측정 (문서의 중요도, 분야의 적합성) 다수의 Source에서 수집된 정보에 대해서 상호 비교

15 Association

16 Global vs Local Extrations
Local Extraction models 하나의 웹사이트로부터 정보를 추출 해당 사이트에 꼭 맞춘 형식화된 XML 스타일로 HTML 문서를 변환 Global Extraction models 많은 웹 사이트의 텍스트로부터 필드화된 정보를 추출 두 모델을 혼합 Local model은 Global model의 학습용 데이터 혹은 정확도가 높은 초기 DB를 추출해 줄 수 있음 Global model은 Local model에서 발생하지 않은 새로운 데이터나 새로운 필드를 추가해 줄 수 있음

17 Information Extraction in Real
CGI로 생성된 HTML 페이지 생성 : DB -> (CGI) -> HTML 리버스엔지니어링 : HTML -> (Crawler) -> (Wrapper) -> DB News, Report 언어적인 분석을 통해서 Entity, Attribute, Fact, Event를 추출하여야 함

18 Extracting Corporate Information
Data automatically extracted from marketsoft.com Source web page. Color highlights indicate type of information. (e.g., red = name) Dun & Bradstreet is the oldest, largest most established seller of business info in the world. They maintain a DB of all 11M US companies, and they do it very inefficiently: phone calls. We are extracting basic company identification information, like name, address, phone, fax, from over 10M domain names. Again, on left, original page, with markup showing where WB extracted the DB fields, which are shown on right. Again, formatting and position on page is very indicative here. Relative position of entities says something about how they go together---which person with which title, etc. E.g., information need: Who is the CEO of MarketSoft? Source: Whizbang! Labs/ Andrew McCallum

19 Product information

20 Product information

21 Canonicalization: Product information

22 Wrappers 에이전트를 이용한 정보추출을 위해서는 각 문서에 대해서 추출하고자 하는 정보의 위치와 구조, 포맷 등을 나타내는 규칙이 필요하며 일반적으로 이러한 규칙을 wrapper라고 한다. Wrapper의 작성 수동 작성 : 정보 추출의 정확성을 높일수 있지만 문서가 변경되면 대책이 없음 자동 생성 : 도메인 지식과 샘플문서를 이용해서 자동 생성, 문서 변경에 대응

23 Amazon Book Description
…. </td></tr> </table> <b class="sans">The Age of Spiritual Machines : When Computers Exceed Human Intelligence</b><br> <font face=verdana,arial,helvetica size=-1> by <a href="/exec/obidos/search-handle-url/index=books&field-author= Kurzweil%2C%20Ray/ "> Ray Kurzweil</a><br> </font> <br> <a href=" <img src=" width=90 height=140 align=left border=0></a> <span class="small"> <b>List Price:</b> <span class=listprice>$14.95</span><br> <b>Our Price: <font color=#990000>$11.96</font></b><br> <b>You Save:</b> <font color=#990000><b>$2.99 </b> (20%)</font><br> </span> <p> <br>…

24 Extracted Book Template
Title: The Age of Spiritual Machines : When Computers Exceed Human Intelligence Author: Ray Kurzweil List-Price: $14.95 Price: $11.96 :

25 Wrappers: Simple Extraction Patterns
Specify an item to extract for a slot using a regular expression pattern. Price pattern: “\b\$\d+(\.\d{2})?\b” May require preceding (pre-filler) pattern to identify proper context. Amazon list price: Pre-filler pattern: “<b>List Price:</b> <span class=listprice>” Filler pattern: “\$\d+(\.\d{2})?\b” May require succeeding (post-filler) pattern to identify the end of the filler. Filler pattern: “.+” Post-filler pattern: “</span>”

26 Wrapper induction Highly regular source documents  Relatively simple extraction patterns  Efficient learning algorithm Writing accurate patterns for each slot for each domain (e.g. each web site) requires laborious software engineering. Alternative is to use machine learning: 학습용 데이터 (문서와 사람이 만든 규칙 pair)를 구축한다. HTML 문서에서 각 항목의 주위에 나타나는 특정 패턴을 자동 학습한다.

27 Wrapper induction: Delimiter-based extraction
<HTML><TITLE>Some Country Codes</TITLE> <B>Congo</B> <I>242</I><BR> <B>Egypt</B> <I>20</I><BR> <B>Belize</B> <I>501</I><BR> <B>Spain</B> <I>34</I><BR> </BODY></HTML>  Use <B>, </B>, <I>, </I> for extraction

28 l1, r1, …, lK, rK labeled pages wrapper Learning LR wrappers
<HTML><HEAD>Some Country Codes</HEAD> <B>Congo</B> <I>242</I><BR> <B>Egypt</B> <I>20</I><BR> <B>Belize</B> <I>501</I><BR> <B>Spain</B> <I>34</I><BR> </BODY></HTML> l1, r1, …, lK, rK Example: Find 4 strings <B>, </B>, <I>, </I>  l1 , r1 , l2 , r2 

29 r1 can be any prefix eg </B>
LR: Finding r1 <HTML><TITLE>Some Country Codes</TITLE> <B>Congo</B> <I>242</I><BR> <B>Egypt</B> <I>20</I><BR> <B>Belize</B> <I>501</I><BR> <B>Spain</B> <I>34</I><BR> </BODY></HTML> r1 can be any prefix eg </B>

30 LR: Finding l1, l2 and r2 r2 can be any prefix eg </I>
<HTML><TITLE>Some Country Codes</TITLE> <B>Congo</B> <I>242</I><BR> <B>Egypt</B> <I>20</I><BR> <B>Belize</B> <I>501</I><BR> <B>Spain</B> <I>34</I><BR> </BODY></HTML> r2 can be any prefix eg </I> l2 can be any suffix eg <I> l1 can be any suffix eg <B>

31 Wrapper 생성기 : 전체 흐름도와 도메인 지식 표현

32 Wrapper 생성기 : 전처리 – 논리라인 생성
브라우저 상에 출력되는 형태처럼 눈에 보이지 않는 HTML 태그를 제거하고 테이블 관련 태그(예를 들어, TR, TH 등)나 라인을 분리할 때 사용되는 리스트형 태그(예를 들어, BR, P, LI)를 기준으로 라인을 분리

33 Wrapper 생성기 : 도메인 지식을 이용해서 논리 라인 의미분석
도메인 지식의 각 OBJECT에 대한 패턴을 논리라인으로부터 찾아서 일치하는 FORMAT을 기록한다.

34 XML 규칙 생성 도메인 지식을 적용해서 HTML에서 특정 패턴에 대한 현상을 XML 문서로 기술하여 XML 파일로 저장한다.

35 Natural Language Processing-based IE
If extracting from more natural, unstructured, human-written text, some NLP may help. Part-of-speech (POS) tagging (품사 태깅) Mark each word as a noun, verb, preposition, etc. Syntactic parsing (명사구, 동사구, 관형어구) Identify phrases: NP, VP, PP Semantic word categories (e.g. from WordNet) KILL: kill, murder, assassinate, strangle, suffocate Extraction patterns can use POS or phrase tags. Crime victim: 누가 [ 죽였다 누구를] Prefiller: [POS: V, Hypernym: KILL] Filler: [Phrase: NP]

36 Finite state automata transductions
Pattern-maching PN ’s (ADJ)* N P Art (ADJ)* N {PN ’s | Art}(ADJ)* N (P Art (ADJ)* N)* 1 2 3 4 PN ’s ADJ Art N P John’s interesting book with a nice cover

37 Rule-based Extraction Examples
Determining which person holds what office in what organization [person] , [office] of [org] Vuk Draskovic, leader of the Serbian Renewal Movement [org] (named, appointed, etc.) [person] P [office] NATO appointed Wesley Clark as Commander in Chief Determining where an organization is located [org] in [loc] NATO headquarters in Brussels [org] [loc] (division, branch, headquarters, etc.) KFOR Kosovo headquarters

38 Three generations of IE systems
Hand-Built Systems – Knowledge Engineering [1980s– ] 규칙을 직접 작성 해당 분야와 정보추출 시스템에 능통한 전문가가 필요 { 추측 – 실험 -변경 } 을 반복함 Automatic, Trainable Rule-Extraction Systems [1990s– ] 미리 정의된 템플렛을 이용해서 규칙을 자동으로 발견하는 시스템 대규모의 labeled corpora가 필요 Statistical Generative Models [1997 – ] 문서에서 연관성이 있는 부분을 찾아내는 통계적인 모델 이용 - using HMMs or statistical parsers Learning usually supervised; may be partially unsupervised

39 Evaluating IE Accuracy
시스템 개발에서 사용되지 않은 사람이 직접 만든 테스트 데이터를 사용하여 성능을 측정 Template Measure for each test document: Total number of correct extractions in the solution template: N Total number of slot/value pairs extracted by the system: E Number of extracted slot/value pairs that are correct (i.e. in the solution template): C Compute average value of metrics adapted from IR: Recall = C/N Precision = C/E F-Measure = Harmonic mean of recall and precision

40 MUC: the genesis of IE DARPA funded significant efforts in IE in the early to mid 1990’s. Message Understanding Conference (MUC) was an annual event/competition where results were presented. Focused on extracting information from news articles: Terrorist events Industrial joint ventures Company management changes Information extraction of particular interest to the intelligence community (CIA, NSA). 참조 사이트

41 MUC Information Extraction: State of the Art c. 1997
NE – named entity recognition CO – coreference resolution TE – template element construction TR – template relation construction ST – scenario template production

42 Basic IE References Douglas E. Appelt and David Israel Introduction to Information Extraction Technology. IJCAI 1999 Tutorial. Kushmerick, Weld, Doorenbos: Wrapper Induction for Information Extraction,IJCAI Stephen Soderland: Learning Information Extraction Rules for Semi-Structured and Free Text. Machine Learning 34(1-3): (1999)