information extraction
TRANSCRIPT
Text Mining Course • 1) Introduction to Text Mining • 2) Introduction to NLP • 3) Named Entity Recognition and Disambiguation • 4) Opinion Mining and Sentiment Analysis • 5) Information Extraction
• 6) NewsReader and Visualisation • 7) Guest Lecture and Q&A
Outline 1. What is Information Extraction 2. Main goals of Information Extraction 3. Information Extraction Tasks and Subtasks 4. MUC conferences 5. Main domains of Information Extraction 6. Methods for Information Extraction
o Cascaded finite-state transducers o Regular expressions and patterns o Supervised learning approaches o Weakly supervised and unsupervised approaches
7. How far we are with IE
What is IE? • Late 1970s within NLP field
• Find and extract automatically limited relevant parts of texts
• Merge information from many pieces of text
What is IE? • Quite often in specialized domains
• Move from unstructured/semi-structured data to structured data o Schemas o Relations (as a database) o Knowledge base o RDF triples
What is IE? Unstructured text
• Natural language sentences • Historically NLP system have been designed to process this type of data • The meaning à linguistic analysis and natural language understanding
What is IE? Semi-‐‑structured text
• The physical layout helps to the interpretation • Processing half way linguistic features ßà positional features
What is IE?
Main goals of IE • Fill a predefined “template” from raw text
• Extract who did what to whom and when? o Event extraction
• Organize information so that is useful to people
• Put information in a form that allows further inferences by computers o Big data
IE. Task & Subtasks • Named Entity Recognition
o Detection à Mr. Smith eats bitterballen [Mr. Smith] : ENTITY o Classification à Mr. Smith eats bitterballen [Mr. Smith] : PERSON
• Event extraction o The thief broke the door with a hammer
• CAUSE_HARMà Verb: break Agent: the thief Patient: the door Instrument: a hammer
• Coreference resolution o [Mr. Smith] eats bitterballen. Besides to this, [he] only drinks Belgium beer.
IE. Task & Subtasks • Relationship extraction
o Bill works for IBM PERSON works for ORGANISATION
• Terminology extraction o Finding relevant terms of multi words from a given corpus
• Some concrete examples o Extracting earnings, profits, board members, headquarters from company
reports o Searching on the WWW for e-mails for advertising (spamming) o Learn drug-gene product interactions from biomedical research papers
IE Tasks & Subtasks • Apple mail
MUC conferences • Message Understanding Conference (MUC), held
between 1987 and 1998.
• Domain specific texts + training examples + template definition
• Precision, Recall and F1 as evaluation
• Domains o MUC-1 (1987), MUC-2 (1989): Naval operations messages. o MUC-3 (1991), MUC-4 (1992): Terrorism in Latin American countries. o MUC-5 (1993): Joint ventures and microelectronics domain. o MUC-6 (1995): News articles on management changes. o MUC-7 (1998): Satellite launch reports.
MUC conferences 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. The joint venture, Bridgestone Sports Taiwan Co., 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.
Example from MUC5
Main domains of IE • Terrorist events
• Joint ventures
• Plane crashes
• Disease outbreaks
• Seminar announcements
• Biological and medical domain
Outline 1. What is Information Extraction 2. Main goals of Information Extraction 3. Information Extraction Tasks and Subtasks 4. MUC conferences 5. Main domains of Information Extraction 6. Methods for Information Extraction
o Cascaded finite-state transducers o Regular expressions and patterns o Supervised learning approaches o Weakly supervised and unsupervised approaches
7. How far we are with IE
Methods for IE • Cascaded finite-state transducers
o Rule based o Regular expressions
• Learning based approaches o Traditional classifiers
• Bayes, MME, SVM … o Sequence label models
• HMM, CMM, CRF
• Unsupervised approaches
• Hybrid approaches
Cascaded finite-‐‑state transducers
• Emerging idea from MUC participants and approaches
• Decompose the task into small sub-tasks
• One element is read at a time from a sequence o Depending on the type a certain transition in produced in the automaton
to a new state
o Some states are considered final (the input matches a certain pattern)
• Can be defined as a regular expression
Cascaded finite-‐‑state transducers
Finite Automaton for noun groups
=> John’s interesting book with a nice cover
Cascaded finite-‐‑state transducers
• Earlier stages recognize smaller linguistics objects o Usually domain independent
• Later stages build on top of the previous ones o Usually domain dependent
• Typical IE systems 1. Complex words 2. Basic phrases 3. Complex phrases 4. Domain events 5. Merging structures
Cascaded finite-‐‑state transducers
• Complex words o Multiwords: “set up” “trading house” o NE: “Bridgestone Sports Co”
• Basic Phrases o Syntactic chunking
• Noun groups (head noun + all modifiers) • Verb groups
Cascaded finite-‐‑state transducers
Cascaded finite-‐‑state transducers
• Complex phrases o Complex noun and verb groups on the basis of syntactic information
• The attachment of appositives to their head noun group o “The joint venture, Bridgestone Sports Taiwan Co.,”
• The construction of measure phrases o “20,000 iron and ‘metal wood’ clubs a month”
Cascaded finite-‐‑state transducers
• Domain events o Recognize events and match with “fillers” detected in previous steps
o Requires domain specific patterns • To recognize phrases of interest • To define what are the roles
o Patterns can be defined also as a finite-state machines or regular expressions
• <Company/ies><Set-up><Joint-Venture> with <Company/ies> • <Company><Capitalized> at <Currency>
Cascaded finite-‐‑state transducers
Regular Expressions • 1950’s Stephen Kleene • A string pattern that describes/matches a set of
strings
• A regular expression consists of: o Characters
o Operation symbols • Boolean (and/or) • Grouping (for defining scopes) • Quantification
Regular Expressions Character Description a The character a . Any single character [abc] Any character in the brackets (OR) ‘a’
or ‘b’ or ‘c’ [^abc]
Any character not in the brackets. Any symbol that is not ‘a ‘ or ‘b’ or ‘c’
* Quantifier. Matches the preceding element ZERO or more times
+ Quantifier. Matches the preceding element ONE or more times
? Matches the previous element zero or one time
| Choice (OR) Matches one of the expressions (before of after the |)
Regular Expressions ① .at è ???
Regular Expressions ① .at è hat cat bat xat … ② [hc]at è hat cat ③ [^b]at è all matched by .at but “bat” ④ [^hc]at è all match by .at but “hat” and
“cat” ⑤ s.* è s sssss ssbsd2ck3e
Regular Expressions ① .at è hat cat bat xat … ② [hc]at è hat cat ③ [^b]at è all matched by .at but “bat” ④ [^hc]at è all match by .at but “hat” and
“cat” ⑤ s.* è s sssss ssbsd2ck3e ⑥ [hc]*at è hat cat hhat chat cchhat at … ⑦ cat|dog è cat dog ⑧ …. ⑨ ….
Using Regular Expressions
• Typically extracting information from automatic generated webpages is easy
o Wikipedia
• To know the country for a given city o Amazon webpage
• From a list of hits
o Weather forecast webpages
o DBpedia
Using Regular Expressions
Using Regular Expressions
• Some “unstructured” pieces of information keep some structure and are easy to capture by means of regular expressions o Phone numbers
o What else?
o …
o ...
Using Regular Expressions
• Some “unstructured” pieces of information keep some structure and are easy to capture by means of regular expressions o Phone numbers
o E-mails
o URL Websites
Using Regular Expressions
• Also to detect relations and fill events
• Higher level regular expressions make use of “objects” detected by lower level patterns
• Some NLP information may help (pos tags, phrases, semantic word categories) o Crime-Victim can use things matched by “noun-group”
• Prefiller: [pos: V, type-of-verb: KILL] WordNet MCR • Filler: [phrase: NOUN-GROUP]
Using Regular Expressions
• Extraction relations between entities o Which PERSON holds what POSITION in what ORGANIZATION
• [PER], [POSITION] of [ORG]
Entities: PER: Jose Mourinho POSITION: trainer ORG: Chelsea
Relation
Jose Mourinho Trainer
Chelsea
Using Regular Expressions
• Extraction relations between entities o Which PERSON holds what POSITION in what ORGANIZATION
• [PER], [POSITION ] of [ORG] • [ORG] (named, appointed,…) [PER] Prep [POSITION]
o Nokia has appointed Rajeev Suri as President
o Where a ORGANIZATION is located
• [ORG] headquarters in [LOC] o NATO headquarters in Brussels
• [ORG][LOC] (division, branch, headquarters…) o KFOR Kosovo headquarters
Extracting relations with palerns
• Hearst 1992
• What does Gelidium mean?
• “Αγαρ ισ α συβστανχε πρεπαρεδ φροµ α µιξτυρε οφ ρεδ αλγαε, συχη ασ
Gelidium, φορ λαβορατορψ ορ ινδυστριαλ υσε”
Extracting relations with palerns
• Hearst 1992
• What does Gelidium mean?
• “Agar is a substance prepared from a mixture of red algae, such as Gelidium, for laboratory or industrial use”
• How do you know?
Extracting relations with palerns
• Hearst 1992: Automatic Acquisition of Hyponyms (IS-A)
X à Gelidium (sub-type) Y à red algae (super-type) X à IS-A à Y
• “Y such as X” • “Y, such as X” • “X or other Y” • “X and other Y” • “Y including X” • ….
Extracting relations with palerns
Hand-‐‑built palerns • Positive
o Tend to be high-precision o Can be adapted to specific domains
• Negative o Human patterns are usually low-recall o A lot of work to think all possible patterns o Need to create a lot of patterns for every relation
Learning-‐‑based Approaches
• Statistical techniques and machine learning algorithms o Automatically learn patterns and models for new domains
• Some types o Supervised learning of patterns and rules o Supervised Learning for relation extraction o Supervised learning of Sequential Classifier Methods o Weakly supervised and supervised
Supervised Learning of Palerns and Rules
• Aiming to reduce the knowledge engineering bottleneck to create an IE in a new domain
• AutoSlog and PALKA à first IE pattern learning systems o AutoSlog: syntactic templates, lexico-syntactic patterns and manual
review
• Learning Algorithms à generate rules from annotated text o LIEP (Huffman 1996) : syntactic paths, role fillers. Patterns that work ok in
training are kept o (LP)2 uses tagging rules and correction rules
Supervised Learning of Palerns and Rules
• Relational learning methods o RAPIER: rules for pre-filler, filler, and post-filler component. Each
component is a pattern that consists of words, POS tags, and semantic classes.
Supervised Learning for relation extraction (I)
• Design a supervised machine learning framework
• Decide what relations we are interested in
• Choose what entities are relevant
• Find (or create) labeled data o Representative corpus o Label the entities in the corpus (Automatic NER) o Hand label relation between these entities o Split into train + dev + test
• Train, improve and evaluate
Supervised Learning for relation extraction (II)
• Relation extraction as a classification problem • 2 classifiers
o To decide if two entities are related o To decide the class for a pair or related entities
• Why 2? o Faster training by eliminating most pairs
o Appropriate feature sets for each task
• Find all pairs of NE (restricted to the sentence) o For every pair
1. Are the entities related (classifier 1) 1. no à END 2. Yes à guess the class (classifier 2)
Supervised Learning for relation extraction (III)
• Are the two entities related? • What is the type of relation?
Supervised Learning for relation extraction (IV)
“[American Airlines], a unit of AMR, immediately matched the move, spokesman [Tim Wagner] said” • What features?
o Head words of entity mentions and combination • Airlines Wagner Airlines-Wagner
o Bag-of-words in the two entity mentions • American, Airlines, Tim, Wagner, American Airlines, Tim Wagner
o Words/bigrams in particular positions to the left and right • M2#-1: spokesman M1#+1: said
o Bag-of-words (or bigrams) between the 2 mentions • a, AMR, of, immediately, matched, move, spokesman, the, unit
Supervised Learning for relation extraction (V)
“[American Airlines], a unit of AMR, immediately matched the move, spokesman [Tim Wagner] said” • What features?
o Named entity types • M1: ORG M2: PERSON
o Entity level (Name, Nominal (NP), Pronoun) • M1: NAME (“it” or “he” would be PRONOUN) • M2: NAME (“the company” would be NOMINAL)
o Basic chunk sequence from one entity to the other • NP NP PP VP NP NP
o Constituency path on the parse tree • NP é NP é S é S ê NP
Supervised Learning for relation extraction (VI)
“[American Airlines], a unit of AMR, immediately matched the move, spokesman [Tim Wagner] said” • What features?
• Trigger lists o For family à parent, wife, husband… (WordNet)
• Gazetteers o List of countries…
• …. • …. • …
Supervised Learning for relation extraction (VII)
• Decide your algorithm o MaxEnt, Naïve Bayes, SVM
• Train the system on the training data
• Tune it on the dev set
• Test on the evaluation test o Traditional Precision, Recall and F-score
Sequential Classifier Methods
• IE as a classification problem using sequential learning models.
• A classifier is induced from annotated data to sequentially scan a text from left to right and decide what piece of text must be extracted or not
• Decide what you want to extract
• Represent the annotated data in a proper way
Sequential Classifier Methods
Sequential Classifier Methods
• Typical steps for training o Get the annotated training data o Represent the data in IOB o Design feature extractors o Decide the algorithm to use o Train the models
• Testing steps o Get the test documents o Extract features o Run the sequence models o Extract the recognized entities
Sequential Classifier Methods
• Algorithms o HMM o CMM o CRF
• Features o Words (current, previous, next) o Other linguistic information (PoS, chunks…) o Task specific features (NER…)
• Word shapes: abstract representation for words
Sequential Classifier Methods
• Algorithms o HMM o SVM o CRF
• Features o Words (current, previous, next) o Other linguistic information (PoS, chunks…) o Task specific features (NER…)
• Word shapes: abstract representation for words
Weakly supervised and unsupervised
• Manual annotation is also “expensive” o IE is quite domain specific à not reuse
• AutoSlog-Ts: o Just needs 2 sets of documents: relevant/irrelevant o Syntactic templates + relevance according to relevant set
• Ex-Disco (Yangarber et al. 2000) o No need preclassified corpus o They use a small set of patterns to decide relevant/irrelevant
Weakly supervised and unsupervised
• OpeNER: • European project dealing with entity recognition,
sentiment analysis and opinion mining mainly in hotel reviews (also restaurants, attractions, news)
• Double propagation o Method to automatically gather opinion words and targets
• From a large raw hotel corpus • Providing a set of seeds and patterns
Weakly supervised and unsupervised
• Seed list • + à good, nice • - à bad, ugly
• Patterns • a [EXP] [TAR] • the [EXP] [TAR]
• Polarity patterns • = [EXP] and [EXP] [EXP], [EXP] • ! [EXP] but [EXP]
Weakly supervised and unsupervised
• Propagation method o 1) Get new targets using the seed expressions and the
patterns • a nice [TAR] a bad [TAR] the ugly [TAR] • Output à new targets (hotel, room, location)
o 2) Get new expression using the previous targets and the patterns • a [EXP] hotel the [EXP] location • Output à new expressions (expensive, cozy, perfect…)
o Keep running 1 and 2 to get new EXP and TAR
Weakly supervised and unsupervised
• Polarity guessing o Apply the polarity patters to guess the polarity
• = a nice(+) and cozy(?) à cozy(+) • ! Clean(+) but expensive(?) à expensive (-)
hlps://github.com/opener-‐‑project/opinion-‐‑domain-‐‑lexicon-‐‑acquisition
Outline 1. What is Information Extraction 2. Main goals of Information Extraction 3. Information Extraction Tasks and Subtasks 4. MUC conferences 5. Main domains of Information Extraction 6. Methods for Information Extraction
o Cascaded finite-state transducers o Regular expressions and patterns o Supervised learning approaches o Weakly supervised and unsupervised approaches
7. How far we are with IE
How good is IE
How good is IE • Some progress has been done • Still the barrier of 60% seems difficult to outperform • Most errors on entities and event coreference • Propagation errors
o Entity recognition à 90% o One event -> 4 entities o 0.9 x 4 à 60%
• A lot of knowledge is implicit or “common world knowledge”
How good is IE Information Type Accuracy Entities 90 – 98% Alributes 80% Relations 60 – 70% Events 50 – 60%
• Very optimistic numbers for well-established tasks • The numbers go down for specific/new tasks
