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Opinion Mining
A Short Tutorial
Kavita Ganesan
Hyun Duk Kim
(http://www.kavita-ganesan.com/)
(https://sites.google.com/site/gildong2/)
Text Information Management Group
University of Illinois @ Urbana Champaign
Agenda
 Introduction
 Application Areas
 Sub-fields of Opinion Mining
 Some Basics
 Opinion Mining Work
 Sentiment Classification
 Opinion Retrieval
“What people think?”
What others think has always been an important piece of information
“Which car should I buy?”
“Which schools should I
apply to?”
“Which Professor to work for?”
“Whom should I vote for?”
“So whom shall I ask?”
Pre Web
 Friends and relatives
 Acquaintances
 Consumer Reports
Post Web
“…I don’t know who..but apparently it’s a good phone. It has good battery life and…”
 Blogs (google blogs, livejournal)
 E-commerce sites (amazon, ebay)
 Review sites (CNET, PC Magazine)
 Discussion forums (forums.craigslist.org,
forums.macrumors.com)
 Friends and Relatives (occasionally)
“Whoala! I have the reviews I need”
Now that I have “too much” information on one
topic…I could easily form my opinion and make
decisions…
Is this true?
…Not Quite
 Searching for reviews may be difficult
 Can you search for opinions as conveniently
as general Web search?
eg: is it easy to search for “iPhone vs Google Phone”?
 Overwhelming amounts of information on one
topic
 Difficult to analyze each and every review
 Reviews are expressed in different ways
“the google phone is a disappointment….”
“don’t waste your money on the g-phone….”
“google phone is great but I expected more in terms of…”
“…bought google phone thinking that it would be useful but…”
“Let me look at reviews on one site only…”
Problems?
 Biased views
 all reviewers on one site may have the same opinion
 Fake reviews/Spam (sites like YellowPages, CitySearch are prone to
this)
 people post good reviews about their own product OR
services
 some posts are plain spams
Coincidence or Fake?
Reviews for a moving
company from YellowPages
 # of merchants
reviewed by the each of
these reviewers  1
 Review dates close
to one another
 All rated 5 star
 Reviewers seem to know
exact names of people
working in the company and
TOO many positive mentions
So where does all of this lead to?
Heard of these terms?
Opinion Mining
Review Mining
Sentiment Analysis
Appraisal Extraction
Subjectivity Analysis
Synonymous
&
Interchangeably Used!
So, what is Subjectivity?
 The linguistic expression of somebody’s opinions,
sentiments, emotions…..(private states)
 private state: state that is not open to objective verification
(Quirk, Greenbaum, Leech, Svartvik (1985). A Comprehensive Grammar of the English Language.)
 Subjectivity analysis - is the computational study of
affect, opinions, and sentiments expressed in text
 blogs
 editorials
 reviews (of products, movies, books, etc.)
 newspaper articles
Example: iPhone review
CNET review
Review on InfoWorld -
tech news site
Review posted on a tech blog
InfoWorld
-summary is structured
-everything else is plain text
-mixture of objective and
subjective information
-no separation between
positives and negatives
CNET
-nice structure
-positives and negatives
separated
Tech BLOG
-everything is plain text
-no separation between
positives and negatives
Example: iPhone review
CNET review
Review on InfoWorld -
tech news site
Review posted on a tech blog
Subjectivity Analysis on iPhone
Reviews
Individual’s Perspective
 Highlight of what is good and bad about iPhone
 Ex. Tech blog may contain mixture of information
 Combination of good and bad from the different
sites (tech blog, InfoWorld and CNET)
 Complementing information
 Contrasting opinions
Ex.
CNET: The iPhone lacks some basic features
Tech Blog: The iPhone has a complete set of features
Subjectivity Analysis on iPhone
Reviews
Business’ Perspective
 Apple: What do consumers think about iPhone?
 Do they like it?
 What do they dislike?
 What are the major complaints?
 What features should we add?
 Apple’s competitor:
 What are iPhone’s weaknesses?
 How can we compete with them?
 Do people like everything about it?
Known as Business
Intelligence
Opinion Trend (temporal) ?
Sentiments for a given product/brand/services
Business Intelligence
Software
Business Intelligence
Software
Other examples
 Blog Search
http://www.blogsearchengine.com/blog-search/?q=ob
 Forum Search
http://www.boardtracker.com/
Application Areas Summarized
 Businesses and organizations: interested in opinions
 product and service benchmarking
 market intelligence
 survey on a topic
 Individuals: interested in other’s opinions when
 Purchasing a product
 Using a service
 Tracking political topics
 Other decision making tasks
 Ads placements: Placing ads in user-generated content
 Place an ad when one praises an product
 Place an ad from a competitor if one criticizes a product
 Opinion search: providing general search for opinions
Opinion Mining – The Big Picture
Opinion Retrieval Opinion Question
Answering
Sentiment Classification
Opinion
Spam/Trustworthiness
Comparative mining
Sentence Level
Document Level
Feature Level
use one or combination
Opinion Mining
Direct Opinions
Opinion Integration
IR IR
Some basics…
 Basic components of an opinion
1. Opinion holder: The person or organization that holds a
specific opinion on a particular object
2. Object: item on which an opinion is expressed
3. Opinion: a view, attitude, or appraisal on an object from an
opinion holder.
This is a great
book
Opinion
Opinion Holder
Object
Some basics…
 Two types of evaluations
Direct opinions
“This car has poor mileage”
Comparisons
“The Toyota Corolla is not as good as Honda Civic”
 They use different language constructs
 Direct opinions are easier to work with but comparisons
may be more insightful
An Overview of the Sub Fields
Sentiment Classification
Comparative mining
Classify sentence/document/feature
based on sentiments expressed by
authors
positive, negative, neutral
Classify sentence/document/feature
based on sentiments expressed by
authors
positive, negative, neutral
Identify comparative sentences & extract
comparative relations
Comparative sentence:
“Canon’s picture quality is better than that of
Sony and Nikon”
Comparative relation:
(better, [picture quality], [Canon], [Sony, Nikon])
Identify comparative sentences & extract
comparative relations
Comparative sentence:
“Canon’s picture quality is better than that of
Sony and Nikon”
Comparative relation:
(better, [picture quality], [Canon], [Sony, Nikon])
relation feature entity1 entity2
An Overview of the Sub Fields
Opinion Integration
Opinion
Spam/Trustworthiness
Automatically integrate opinions
from different sources such as
expert review sites, blogs and
forums
Automatically integrate opinions
from different sources such as
expert review sites, blogs and
forums
Try to determine likelihood of spam in
opinion and also determine authority
of opinion
Ex. of Untrustworthy opinions:
 Repetition of reviews
 Misleading “positive” opinion
 High concentration of certain words
Try to determine likelihood of spam in
opinion and also determine authority
of opinion
Ex. of Untrustworthy opinions:
 Repetition of reviews
 Misleading “positive” opinion
 High concentration of certain words
Opinion Retrieval
 Analogous to document retrieval
process
 Requires documents to be retrieved
and ranked according to opinions
about a topic
 A relevant document must satisfy the
following criteria:
 relevant to the query topic
 contains opinions about the
query
 Analogous to document retrieval
process
 Requires documents to be retrieved
and ranked according to opinions
about a topic
 A relevant document must satisfy the
following criteria:
 relevant to the query topic
 contains opinions about the
query
An Overview of the Sub Fields
Opinion Question
Answering
Similar to opinion retrieval task, only that
instead of returning a set of opinions,
answers have to be a summary of those
opinions and format has to be in “natural
language” form
Ex.
Q: What is the international reaction to
the reelection of Robert Mugabe as
president of Zimbabwe?
A: African observers generally approved of
his victory while Western Governments
strongly denounced it.
Similar to opinion retrieval task, only that
instead of returning a set of opinions,
answers have to be a summary of those
opinions and format has to be in “natural
language” form
Ex.
Q: What is the international reaction to
the reelection of Robert Mugabe as
president of Zimbabwe?
A: African observers generally approved of
his victory while Western Governments
strongly denounced it.
Agenda
 Introduction
 Application Areas
 Sub-fields of Opinion Mining
 Some Basics
Opinion Mining Work
 Sentiment Classification
 Opinion Retrieval
Where to find details of previous work?
“Web Data Mining” Book, Bing Liu, 2007
“Opinion Mining and Sentiment Analysis” Book,
Bo Pang and Lillian Lee, 2008
What is Sentiment Classification?
 Classify sentences/documents (e.g. reviews)/features
based on the overall sentiments expressed by authors
 positive, negative and (possibly) neutral
 Similar to topic-based text classification
 Topic-based classification: topic words are important
 Sentiment classification: sentiment words are more important
(e.g: great, excellent, horrible, bad, worst)
A. Sentence Level Classification
 Assumption: a sentence contains only one opinion (not
true in many cases)
 Task 1: identify if sentence is opinionated
classes: objective and subjective (opinionated)
 Task 2: determine polarity of sentence
classes: positive, negative and neutral
Sentiment Classification
Quiz:
“This is a beautiful bracelet..”
Is this sentence subjective/objective?
Is it positive, negative or neutral?
Sentiment Classification
B. Document(post/review) Level Classification
 Assumption:
 each document focuses on a single object (not true in
many cases)
 contains opinion from a single opinion holder (not true
in many cases)
 Task: determine overall sentiment orientation in
document
classes: positive, negative and neutral
Sentiment Classification
C. Feature Level Classification
Goal: produce a feature-based opinion summary of multiple
reviews
 Task 1: Identify and extract object features that have been
commented on by an opinion holder (e.g. “picture”,“battery
life”).
 Task 2: Determine polarity of opinions on features
classes: positive, negative and neutral
 Task 3: Group feature synonyms
Example: Feature Level Classification –
Camera Review
Sentiment Classification
 In summary, approaches used in sentiment classification
 Unsupervised – eg: NLP pattern @ NLP patterns with lexicon
 Supervised – eg: SVM, Naive Bayes..etc (with varying
features like POS tags, word phrases)
 Semi Supervised – eg: lexicon+classifier
 Based on previous work, four features generally used
a. Syntactic features
b. Semantic features
c. Link-based features
d. Stylistic features
 Semantic & Syntactic features are most commonly used
Sentiment Classification
Features Usually Considered
A. Syntatic Features
 What is syntactic feature? - Usage of principles and rules for
constructing sentences in natural languages [wikipedia]
 Different usage of syntactic features:
POS+punctuation
[Pang et al. 2002; Gamon
2004]
POS Pattern
[Nasukawa and Yi 2003; Yi et
al. 2003; Fei et al. 2004;
Wiebe et al 2004]
Modifiers
Whitelaw et al. [2005]
>> POS (part-of-speech) tags
& punctuation
eg: a sentence containing
an adjective and “!” could
indicate existence of an
opinion
“the book is great !”
>>POS n-gram patterns
patterns like “n+aj” (noun
followed by +ve adjective) -
represents positive sentiment
patterns like “n+dj” (noun
followed by -ve adjective) -
express negative sentiment
>> Used a set of modifier
features (e.g., very, mostly,
not)
 the presence of these
features indicate the presence
of appraisal
“the book is not great”
“..this camera is very handy”
Sentiment Classification
Features Usually Considered
B. Semantic Features
 Leverage meaning of words
 Can be done manually/semi/fully automatically
Score Based - Turney [2002] Lexicon Based - Whitelaw et al. [2005]
 Use PMI calculation to compute the SO
score for each word/phrase
 Idea: If a phrase has better association
with the word “Excellent” than with
“Poor” it is positively oriented
and vice versa
Score computation:
PMI (phrase ^ “excellent”) –
PMI (phrase ^ “poor”)
PMI- is a measure of association used in
information theory.
The PMI of a pair of x and y belonging to discrete random
variables quantifies the discrepancy between the probability of
their coincidence given their joint distribution versus the
probability of their coincidence given only their individual
distributions and assuming independence.
 Use appraisal groups for assigning
semantics to words/phrases
 Each phrase/word is manually
classified into various appraisal classes
(eg: deny, endorse, affirm)
Sentiment Classification
Features Usually Considered
C. Link-Based Features
 Use link/citation analysis to determine sentiments of documents
 Efron [2004] found that opinion Web pages heavily linking to each
other often share similar sentiments
 Not a popular approach
D. Stylistic Features
 Incorporate stylometric/authorship studies into sentiment classification
 Style markers have been shown highly prevalent in Web discourse
[Abbasi and Chen 2005; Zheng et al. 2006; Schler et al. 2006]
 Ex. Study the blog authorship style of “Students vs Professors”
Authorship Style of
Students
Authorship Style of
Professors
Colloquial@spoken style of
writing
Formal way of writing
Improper punctuation Proper punctuation
More usage of curse words &
abbreviations
Limited curse words &
abbreviation
Sentiment Classification – Recent Work
Abbasi, Chen & Salem (TOIS-08)
 Propose:
 sentiment analysis of web forum opinions in multiple languages
(English and Arabic)
 Motivation:
 Limited work on sentiment analysis on Web forums
 Most studies have focused on sentiment classification of a
single language
 Almost no usage of stylistic feature categories
 Little emphasis has been placed on feature reduction/selection
techniques
 New:
 Usage of stylistic and syntactic features of English and Arabic
 Introduced new feature selection algorithm: entropy weighted
genetic algorithm (EWGA)
 EWGA outperforms no feature selection baseline, GA and
Information Gain
 Results, using SVM indicate a high level of classification accuracy
Sentiment Classification – Recent Work
Abbasi, Chen & Salem (TOIS-08)
Sentiment Classification – Recent Work
Abbasi, Chen & Salem (TOIS-08)
Sentiment Classification – Recent Work
Abbasi, Chen & Salem (TOIS-08)
Sentiment Classification – Recent Work
Blitzer et al. (ACL 2007)
 Propose:
 Method for domain adaptation for sentiment classifiers (ML
based) focusing on online reviews for different types of
products
 Motivation:
 Sentiments are expressed differently in different domains -
annotating corpora for every domain is impractical
 If you train on the “kitchen” domain and classify on “book”
domain  error increases
 New:
 Extend structural correspondence learning algorithm (SCL) to
sentiment classification area
 Key Idea:
 If two topics/sentences from different domains have high correlation
on unlabeled data, then we can tentatively align them
 Achieved 46% improvement over a supervised baseline for
sentiment classification
Sentiment Classification – Recent Work
Blitzer et al. (ACL 2007)
• Do not buy the Shark portable
steamer …. Trigger mechanism is
defective.
• the very nice lady assured me that I
must have a defective set …. What
a disappointment!
• Maybe mine was defective …. The
directions were unclear
Unlabeled kitchen contexts
• The book is so repetitive that I
found myself yelling …. I will
definitely not buy another.
• A disappointment …. Ender
was talked about for <#> pages
altogether.
• it’s unclear …. It’s repetitive and
boring
Unlabeled books contexts
Aligning sentiments from
different domains
Sentiment Classification - Summary
 Relatively focused & widely researched area
 NLP groups
 IR groups
 Machine Learning groups (e.g., domain adaptation)
 Important because:
 With the wealth of information out on the web, we need an easy
way to know what people think about a certain “topic” – e.g.,
products, political issues, etc
 Heuristics generally used:
 Occurrences of words
 Phrase patterns
 Punctuation
 POS tags/POS n-gram patterns
 Popularity of opinion pages
 Authorship style
Quiz
Can you think of other heuristics to
determine the polarity of subjective
(opinionated) sentences?
Opinion Retrieval
 Is the task of retrieving documents according to topic and
ranking them according to opinions about the topic
 Important when you need people’s opinion on certain topic or
need to make a decision, based on opinions from others
General Search Opinion Search
search for facts search for opinions/opinionated
topics
rank pages according to some
authority and relevance scores
Rank is based on relevance to
topic and content of opinion
Opinion Retrieval
 “Opinion retrieval” started with the work of Hurst
and Nigam (2004)
 Key Idea: Fuse together topicality and polarity
judgment  “opinion retrieval”
 Motivation: To enable IR systems to select content
based on a certain opinion about a certain topic
 Method:
 Topicality judgment: statistical machine learning
classifier (Winnow)
 Polarity judgment: shallow NLP techniques (lexicon
based)
 No notion of ranking strategy
Opinion Retrieval
Summary of TREC Blog Track (2006 – 2008)
TREC 2006 Blog
Track
TREC 2007 Blog Track TREC 2008 Blog Track
Opinion RetrievalOpinion Retrieval Same as 2006 with 2 new
tasks:
-blog distillation (feed search)
-polarity determination
Same as 2006 and 2007
with 1 new task:
-Baseline blog post
retrieval task (i.e. “Find
me blog posts about
X.”)
 TREC-2006 Blog Track – Focus is on Opinion Retrieval
 14 participants
 Baseline System
 A standard IR system without any opinion finding layer
 Most participants use a 2 stage approach
Opinion Retrieval
Summary of TREC-2006 Blog Track [6]
Ranked
documents
standard retrieval &
ranking scheme
Query
opinion related
re-ranking/filterRanked
opinionated
documents
STAGE 1
STAGE 2
-tf*idf
-language model
-probabilistic
-dictionary based
-text classification
-linguistics
Opinion Retrieval
Summary of TREC-2006 Blog Track [6]
 TREC-2006 Blog Track
 The two stage approach
First stage
 documents are ranked based on topical relevance
 mostly off-the-shelf retrieval systems and weighting
models
 TF*IDF ranking scheme
 language modeling approaches
 probabilistic approaches.
Second stage
 results re-ranked or filtered by applying one or more
heuristics for detecting opinions
 Most approaches use linear combination of relevance score
and opinion score to rank documents. eg:
α and β are combination parameters
Opinion Retrieval
Summary of TREC-2006 Blog Track [6]
Opinion detection approaches used:
 Lexicon-based approach [2,3,4,5]:
(a) Some used frequency of certain terms to rank documents
(b) Some combined terms from (a) with information about
the
 distance between sentiment words &
 occurrence of query words in the document
Ex:
Query: “Barack Obama”
Sentiment Terms: great, good, perfect, terrific…
Document: “Obama is a great leader….”
 success of lexicon based approach varied
..of greatest
quality…………
……nice…….
wonderful……
…good battery
life…
..of greatest
quality…………
……nice…….
wonderful……
…good battery
life…
Opinion Retrieval
Summary of TREC-2006 Blog Track [6]
Opinion detection approaches used:
 Text classification approach:
 training data:
 sources known to contain opinionated content (eg: product
reviews)
 sources assumed to contain little opinionated content
(eg:news, encyclopedia)
 classifier preference: Support Vector Machines
 Features (discussed in sentiment classification section):
 n-grams of words– eg: beautiful/<ww>, the/worst, love/it
 part-of-speech tags
 Success of this approach was limited
 Due to differences between training data and actual
opinionated content in blog posts
 Shallow linguistic approach:
 frequency of pronouns (eg: I, you, she) or adjectives (eg: great,
tall, nice) as indicators of opinionated content
 success of this approach was also limited
Opinion Retrieval
Highlight: Gilad Mishne (TREC 2006)
Gilad Mishne (TREC 2006)
 Propose: multiple ranking strategies for opinion retrieval in
blogs
 Introduced 3 aspects to opinion retrieval
 topical relevance
 degree to which the post deals with the given topic
 opinion expression
 given a “topically-relevant” blog post, to what degree it
contains subjective (opinionated) information about it
 post quality
 estimate of the quality of a “blog post”
 assumption - higher-quality posts are likely to contain
meaningful opinions
Opinion Retrieval
Highlight: Gilad Mishne (TREC 2006)
Step 1: Is blog post Relevant to Topic?
language
modeling
based retrieval
language
modeling
based retrieval
Ranked
documents
Ranked
documents
Query
blind relevance
feedback [9]
blind relevance
feedback [9]
term proximity
[10,11]
term proximity
[10,11]
• add terms to original query by
comparing language model of top-
retrieved docs  entire collection
• limited to 3 terms
• every word n-gram from the
query treated as a phrase
temporal
properties
temporal
properties
• determine if query is looking for
recent posts
•boost scores of posts published
close to time of the query date
Topic relevance
improvements
Topic relevance
improvements
Opinion Retrieval
Highlight: Gilad Mishne (TREC 2006)
Step 2: Is blog post Opinionated?
 Lexicon-based method- using GeneralInquirer
 GeneralInquirer
 large-scale, manually-constructed lexicon
 assigns a wide range of categories to more than 10,000
English words
 Example of word categories :
 emotional category: pleasure, pain, feel, arousal, regret
 pronoun category: self, our, and you;
“The meaning of a word is its use in the language” - Ludwig Wittgenstein (1958)
Opinion Retrieval
Highlight: Gilad Mishne (TREC 2006)
Step 2: Is blog post Opinionated?
For each post calculate two sentiment related values known as
“opinion level”
Calculate opinion
level
Calculate opinion
level
Blog postBlog post
Extract “topical sentences” from post
to count the opinion-bearing words in
it
Topical sentences:
>sentences relevant to topic
>sentences immediately
surrounding them
“post opinion” level“post opinion” level
“feed opinion” level“feed opinion” level
(# of occurrences of
words from any of “opinion
indicating” categories )
total # of words
Idea:
Feeds containing a fair amount of
opinions are more likely to express
an opinion in any of its posts
Method:
> use entire feed to which the post
belongs
> topic-independent score per feed
estimates the degree to which it
contains opinions (about any topic)
Opinion Retrieval
Highlight: Gilad Mishne (TREC 2006)
Step 3: Is the blog post of good quality?
 A. Authority of blog post: Link-based Authority
 Estimates authority of documents using analysis of the link
structure
 Key Idea:
 placing a link to a page other than your own is like
“recommending” that page
 similar to document citation in the academic world
 Follow Upstill et al (ADCS 2003) - inbound link
degree (indegree) as an approximation
 captures how many links there are to a page
 Post’s authority estimation is based on:
 Indegree of a post p & indegree of post p’s feed
Site ASite A
Site BSite B
Site CSite C
Blog
Post P
Blog
Post P
Authority=Log(indegree=3)
Opinion Retrieval
Highlight: Gilad Mishne (TREC 2006)]
Step 3: Is the blog post of good quality?
 B. Spam Likelihood
 Method 1: machine-learning approach - SVM
 Method 2: text-level compressibility - Ntoulas et al (WWW
2006)
 Determine: How likely is post P from feed F a SPAM
entry?
 Intuition: Many spam blogs use “keyword stuffing”
 High concentration of certain words
 Words are repeated hundreds of times in the same post
and across feed
 When you detect spam post and compress them  high
compression ratios for these feeds
 Higher the compression ratio for feed F, more likely that
post P is splog (Spam Blog)
comp. ratio=(size of uncompressed pg.) / (size of compressed pg.)
Final spam likelihood estimate: (SVM prediction) * (compressibility prediction)
temporal
properties
temporal
properties
Opinion Retrieval
Highlight: Gilad Mishne (TREC 2006)
Step 4: Linear Model
Combination
top
1000
posts
top
1000
posts
1.Topic relevance
language model
1.Topic relevance
language model
blind relevance
feedback [9]
blind relevance
feedback [9]
term proximity
query [10,11]
term proximity
query [10,11]
2.Opinion level2.Opinion level3.Post Quality3.Post Quality
“feed opinion”
level
“feed opinion”
level
“post opinion”
level
“post opinion”
level
spam likelihood
[13]
spam likelihood
[13]
link based
authority [12]
link based
authority [12]
4. Weighted linear
combination
of scores
4. Weighted linear
combination
of scores
partial “post quality”
scores
partial “opinion level”
scores
ranked
opinionated
posts
ranked
opinionated
posts
final scores
Opinion Retrieval
Summary of TREC-2008 Blog Track
 Opinion Retrieval & Sentiment Classification
 Basic techniques are similar – classification vs. lexicon
 More use of external information source
 Traditional source: WordNet, SentiWordNet
 New source: Wikipedia, Google search result,
Amazon, Opinion web sites (Epinions.com,
Rateitall.com)
Opinion Retrieval
Summary of TREC-2008 Blog Track
 Retrieve ‘good’ blog posts
1. Expert search techniques
 Limit search space by joining data by criteria
 Used characteristics: number of comments, post
length, the posting time
-> estimate strength of association between a post
and a blog.
1. Use of folksonomies
 Folksonomy: collaborative tagging, social indexing.
 User generating taxonomy
 Creating and managing tagging.
 Showed limited performance improvement
Opinion Retrieval
Summary of TREC-2008 Blog Track
 Retrieve ‘good’ blog posts
3. Temporal evidence
 Some investigated use of temporal span and temporal
dispersion.
 Recurring interest, new post.
3. Blog relevancy approach
 Assumption:
 A blog that has many relevant posts is more relevant.
 The top N posts best represent the topic of the blog
 Compute two scores to score a given blog.
 The first score is the average score of all posts in the
blog
 The second score is the average score of the top N
posts that have the highest relevance scores.
 Topic relevance score of each post is calculated using a
language modeling approach.
Opinion Retrieval – Recent Work
He et al (CIKM-08)
 Motivation:
 Current methods require manual effort or external resources
for opinion detection
 Propose:
 Dictionary based statistical approach - automatically derive
evidence of subjectivity
 Automatic dictionary generation – remove too frequent or few
terms with skewed query model
 assign weights – how opinionated. divergence from randomness
(DFR)
 For term w, divergence D(opREl) from D(Rel)
( Retrieved Doc = Rel + nonRel. Rel = opRel + nonOpRel )
 assign opinion score to each document using top weighted terms
 Linear combine opinion score with initial relevance score
 Results:
 Significant improvement over best TREC baseline
 Computationally inexpensive compared to NLP techniques
Zhang and Ye (SIGIR 08)
 Motivation:
 Current ranking uses only linear combination of scores
 Lack theoretical foundation and careful analysis
 Too specific (like restricted to domain of blogs)
 Propose:
 Generation model that unifies topic-relevance and
opinion generation by a quadratic combination
 Relevance ranking serves as weighting factor to
lexicon based sentiment ranking function
 Different than the popular linear combination
Opinion Retrieval – Recent Work
Zhang and Ye (SIGIR 08)
 Key Idea:
 Traditional document generation model:
 Given a query q, how well the document d “fits” the query q
 estimate posterior probability p(d|q)
 In this opinion retrieval model, new sentiment parameter, S
(latent variable) is introduced
Iop(d,q,s): given query q, what is the probability that document d
generates a sentiment expression s
 Tested on TREC Blog datasets – observed significant improvement
Opinion Retrieval – Recent Work
Opinion Generation Model Document Generation Model
Challenges in opinion mining
Summary of TREC Blog Track focus (2006 – 2008)
TREC 2006 Blog
Track
TREC 2007 Blog Track TREC 2008 Blog Track
Opinion RetrievalOpinion Retrieval Same as 2006 with 2 new
tasks:
-blog distillation (feed search)
-polarity determination
Same as 2006 and 2007
with 1 new task:
-Baseline blog post
retrieval task (i.e. “Find
me blog posts about
X.”)
Main Lessons Learnt from TREC 2006, 2007 & 2008:
Good performance in opinion-finding is strongly dependent
on finding as many relevant documents as possible
regardless of their opinionated nature
 Many Opinion classification and retrieval system could not make
improvements.
 Used same relevant document retrieval model.
Evaluate the performance of opinion module.
 ΔMAP = Opinion finding MAP score with only retrieval system –
Opinion finding MAP score with opinion module.
 A lot of margins to research!!!
Group ΔMAP of Mix ΔMAP of Positive ΔMAP of Negative
KLE 4.86% 6.08% 3.51%
UoGTr -3.77% -4.62% -2.76%
UWaterlooEng -6.70% -1.69% -12.33%
UIC_IR_Group -22.10% 2.12% -49.60%
UTD_SLP_Lab -22.96% -17.51% -29.23%
Fub -55.26% -59.81% -50.18%
Tno -76.42% -75.93% -77.02%
UniNE -43.68 -39.41% -48.49%
Challenges in opinion mining
Summary of TREC Blog Track focus (2006 – 2008)
Challenges in opinion mining
Highlight of TREC-2008 Blog Track
Lee et al. Jia et al. (TREC 2008)
 Propose:
 Method for query dependent opinion retrieval and sentiment
classification
 Motivation:
 Sentiments are expressed differently in different query. Similar
to the Blitzer’s idea.
 New:
 Use external web source to obtain positive and negative
opinionated lexicons.
 Key Idea:
 Objective words: Wikipedia, product specification part of Amazon.com
 Subjective words: Reviews from Amazon.com, Rateitall.com and
Epinions.com
 Reviews rated 4 or 5 out of 5: positive words
 Reviews rated 1 or 2 out of 5: negative words
 Top ranked in Text Retrieval Conference.
Challenges in opinion mining
 Polarity terms are context sensitive.
 Ex. Small can be good for ipod size, but can be bad for LCD monitor size.
 Even in the same domain, use different words depending on target
feature.
 Ex. Long ‘ipod’ battery life vs. long ‘ipod’ loading time
 Partially solved (query dependent sentiment classification)
 Implicit and complex opinion expressions
 Rhetoric expression, metaphor, double negation.
 Ex. The food was like a stone.
 Need both good IR and NLP techniques for opinion mining.
 Cannot divide into pos/neg clearly
 Not all opinions can be classified into two categories
 Interpretation can be changed based on conditions.
 Ex. 1) The battery life is ‘long’ if you do not use LCD a lot. (pos)
2) The battery life is ‘short’ if you use LCD a lot. (neg)
Current system classify the first one as positive and second one as negative.
However, actually both are saying the same fact.
Opinion Retrieval – Summary
 Opinion Retrieval is a fairly broad area (IR, sentiment
classification, spam detection, opinion authority…etc)
 Important:
 Opinion search is different than general web search
 Opinion retrieval techniques
 Traditional IR model + Opinion filter/ranking layer (TREC
2006,2007,2008)
 Some approaches in opinion ranking layer:
 Sentiment: lexicon based, ML based, linguistics
 Opinion authority - trustworthiness
 Opinion spam likelihood
 Expert search technique
 Folksonomies
 Opinion generation model
 Unify topic-relevance and opinion generation into one
model
 Future approach:
 Use opinion as a feature or a dimension of more refined
and complex search tasks
Thank You
Thank You
References
 [1] M. Hurst and K. Nigam, “Retrieving topical sentiments from online document collections,” in
Document Recognition and Retrieval XI, pp. 27–34, 2004.
 [2] Liao, X., Cao, D., Tan, S., Liu, Y., Ding, G., and Cheng X.Combining Language Model with
Sentiment Analysis for Opinion Retrieval of Blog-Post. Online Proceedings of Text Retrieval
Conference (TREC) 2006. http://trec.nist.gov/
 [3] Mishne, G. Multiple Ranking Strategies for Opinion Retrieval in Blogs. Online Proceedings of
TREC, 2006.
 [4] Oard, D., Elsayed, T., Wang, J., and Wu, Y. TREC-2006 at Maryland: Blog, Enterprise, Legal and
QA Tracks. OnlineProceedings of TREC, 2006. http://trec.nist.gov/
 [5] Yang, K., Yu, N., Valerio, A., Zhang, H. WIDIT in TREC-2006 Blog track. Online Proceedings of
TREC, 2006. http://trec.nist.gov/
 [6] Ounis, I., de Rijke, M., Macdonald, C., Mishne, G., and Soboroff, I. Overview of the TREC 2006
Blog Track. In Proceedings of TREC 2006, 15–27. http://trec.nist.gov/
 [7] Min Zhang, Xingyao Ye: A generation model to unify topic relevance and lexicon-based
sentiment for opinion retrieval. SIGIR 2008: 411-418
 [9] J. M. Ponte. Language models for relevance feedback. In Advances in Information Retrieval:
Recent Research from the Center for Intelligent Information Retrieval, 2000.
 [10] D. Metzler and W. B. Croft. A markov random field model for term dependencies. In SIGIR ’05,
2005.
 [11] G. Mishne and M. de Rijke. BoostingWeb Retrieval through Query Operations. In ECIR 2005,
2005.
 [12] T. Upstill, N. Craswell, and D. Hawking. Predicting fame and fortune: Pagerank or indegree? In
ADCS2003, 2003.
 [13] A. Ntoulas, M. Najork, M. Manasse, and D. Fetterly. Detecting spam web pages through
content analysis. In WWW 2006, 2006.
 [14] An Effective Statistical Approach to Blog Post Opinion Retrieval.
Ben He, Craig Macdonald Jiyin He, and Iadh Ounis. In Proceedings of CIKM 2008.
References
 [15] I. Ounis, C. Macdonald and I. Soboroff, Overview of the TREC 2008 Blog Track (notebook
paper), TREC, 2008.
 [16] Y. Lee, S.-H. Na, J. Kim, S.-H. Nam, H.-Y. Jung and J.-H. Lee , KLE at TREC 2008 Blog Track:
Blog Post and Feed Retrieval (notebook paper), TREC, 2008.
 [17] L. Jia, C. Yu and W. Zhang, UIC at TREC 208 Blog Track (notebook paper), TREC, 2008.

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Opinion Mining Tutorial (Sentiment Analysis)

  • 1. Opinion Mining A Short Tutorial Kavita Ganesan Hyun Duk Kim (http://www.kavita-ganesan.com/) (https://sites.google.com/site/gildong2/) Text Information Management Group University of Illinois @ Urbana Champaign
  • 2. Agenda  Introduction  Application Areas  Sub-fields of Opinion Mining  Some Basics  Opinion Mining Work  Sentiment Classification  Opinion Retrieval
  • 3. “What people think?” What others think has always been an important piece of information “Which car should I buy?” “Which schools should I apply to?” “Which Professor to work for?” “Whom should I vote for?”
  • 4. “So whom shall I ask?” Pre Web  Friends and relatives  Acquaintances  Consumer Reports Post Web “…I don’t know who..but apparently it’s a good phone. It has good battery life and…”  Blogs (google blogs, livejournal)  E-commerce sites (amazon, ebay)  Review sites (CNET, PC Magazine)  Discussion forums (forums.craigslist.org, forums.macrumors.com)  Friends and Relatives (occasionally)
  • 5. “Whoala! I have the reviews I need” Now that I have “too much” information on one topic…I could easily form my opinion and make decisions… Is this true?
  • 6. …Not Quite  Searching for reviews may be difficult  Can you search for opinions as conveniently as general Web search? eg: is it easy to search for “iPhone vs Google Phone”?  Overwhelming amounts of information on one topic  Difficult to analyze each and every review  Reviews are expressed in different ways “the google phone is a disappointment….” “don’t waste your money on the g-phone….” “google phone is great but I expected more in terms of…” “…bought google phone thinking that it would be useful but…”
  • 7. “Let me look at reviews on one site only…” Problems?  Biased views  all reviewers on one site may have the same opinion  Fake reviews/Spam (sites like YellowPages, CitySearch are prone to this)  people post good reviews about their own product OR services  some posts are plain spams
  • 8. Coincidence or Fake? Reviews for a moving company from YellowPages  # of merchants reviewed by the each of these reviewers  1  Review dates close to one another  All rated 5 star  Reviewers seem to know exact names of people working in the company and TOO many positive mentions
  • 9. So where does all of this lead to?
  • 10. Heard of these terms? Opinion Mining Review Mining Sentiment Analysis Appraisal Extraction Subjectivity Analysis Synonymous & Interchangeably Used!
  • 11. So, what is Subjectivity?  The linguistic expression of somebody’s opinions, sentiments, emotions…..(private states)  private state: state that is not open to objective verification (Quirk, Greenbaum, Leech, Svartvik (1985). A Comprehensive Grammar of the English Language.)  Subjectivity analysis - is the computational study of affect, opinions, and sentiments expressed in text  blogs  editorials  reviews (of products, movies, books, etc.)  newspaper articles
  • 12. Example: iPhone review CNET review Review on InfoWorld - tech news site Review posted on a tech blog InfoWorld -summary is structured -everything else is plain text -mixture of objective and subjective information -no separation between positives and negatives CNET -nice structure -positives and negatives separated Tech BLOG -everything is plain text -no separation between positives and negatives
  • 13. Example: iPhone review CNET review Review on InfoWorld - tech news site Review posted on a tech blog
  • 14. Subjectivity Analysis on iPhone Reviews Individual’s Perspective  Highlight of what is good and bad about iPhone  Ex. Tech blog may contain mixture of information  Combination of good and bad from the different sites (tech blog, InfoWorld and CNET)  Complementing information  Contrasting opinions Ex. CNET: The iPhone lacks some basic features Tech Blog: The iPhone has a complete set of features
  • 15. Subjectivity Analysis on iPhone Reviews Business’ Perspective  Apple: What do consumers think about iPhone?  Do they like it?  What do they dislike?  What are the major complaints?  What features should we add?  Apple’s competitor:  What are iPhone’s weaknesses?  How can we compete with them?  Do people like everything about it? Known as Business Intelligence
  • 16. Opinion Trend (temporal) ? Sentiments for a given product/brand/services Business Intelligence Software Business Intelligence Software
  • 17. Other examples  Blog Search http://www.blogsearchengine.com/blog-search/?q=ob  Forum Search http://www.boardtracker.com/
  • 18. Application Areas Summarized  Businesses and organizations: interested in opinions  product and service benchmarking  market intelligence  survey on a topic  Individuals: interested in other’s opinions when  Purchasing a product  Using a service  Tracking political topics  Other decision making tasks  Ads placements: Placing ads in user-generated content  Place an ad when one praises an product  Place an ad from a competitor if one criticizes a product  Opinion search: providing general search for opinions
  • 19. Opinion Mining – The Big Picture Opinion Retrieval Opinion Question Answering Sentiment Classification Opinion Spam/Trustworthiness Comparative mining Sentence Level Document Level Feature Level use one or combination Opinion Mining Direct Opinions Opinion Integration IR IR
  • 20. Some basics…  Basic components of an opinion 1. Opinion holder: The person or organization that holds a specific opinion on a particular object 2. Object: item on which an opinion is expressed 3. Opinion: a view, attitude, or appraisal on an object from an opinion holder. This is a great book Opinion Opinion Holder Object
  • 21. Some basics…  Two types of evaluations Direct opinions “This car has poor mileage” Comparisons “The Toyota Corolla is not as good as Honda Civic”  They use different language constructs  Direct opinions are easier to work with but comparisons may be more insightful
  • 22. An Overview of the Sub Fields Sentiment Classification Comparative mining Classify sentence/document/feature based on sentiments expressed by authors positive, negative, neutral Classify sentence/document/feature based on sentiments expressed by authors positive, negative, neutral Identify comparative sentences & extract comparative relations Comparative sentence: “Canon’s picture quality is better than that of Sony and Nikon” Comparative relation: (better, [picture quality], [Canon], [Sony, Nikon]) Identify comparative sentences & extract comparative relations Comparative sentence: “Canon’s picture quality is better than that of Sony and Nikon” Comparative relation: (better, [picture quality], [Canon], [Sony, Nikon]) relation feature entity1 entity2
  • 23. An Overview of the Sub Fields Opinion Integration Opinion Spam/Trustworthiness Automatically integrate opinions from different sources such as expert review sites, blogs and forums Automatically integrate opinions from different sources such as expert review sites, blogs and forums Try to determine likelihood of spam in opinion and also determine authority of opinion Ex. of Untrustworthy opinions:  Repetition of reviews  Misleading “positive” opinion  High concentration of certain words Try to determine likelihood of spam in opinion and also determine authority of opinion Ex. of Untrustworthy opinions:  Repetition of reviews  Misleading “positive” opinion  High concentration of certain words Opinion Retrieval  Analogous to document retrieval process  Requires documents to be retrieved and ranked according to opinions about a topic  A relevant document must satisfy the following criteria:  relevant to the query topic  contains opinions about the query  Analogous to document retrieval process  Requires documents to be retrieved and ranked according to opinions about a topic  A relevant document must satisfy the following criteria:  relevant to the query topic  contains opinions about the query
  • 24. An Overview of the Sub Fields Opinion Question Answering Similar to opinion retrieval task, only that instead of returning a set of opinions, answers have to be a summary of those opinions and format has to be in “natural language” form Ex. Q: What is the international reaction to the reelection of Robert Mugabe as president of Zimbabwe? A: African observers generally approved of his victory while Western Governments strongly denounced it. Similar to opinion retrieval task, only that instead of returning a set of opinions, answers have to be a summary of those opinions and format has to be in “natural language” form Ex. Q: What is the international reaction to the reelection of Robert Mugabe as president of Zimbabwe? A: African observers generally approved of his victory while Western Governments strongly denounced it.
  • 25. Agenda  Introduction  Application Areas  Sub-fields of Opinion Mining  Some Basics Opinion Mining Work  Sentiment Classification  Opinion Retrieval
  • 26. Where to find details of previous work? “Web Data Mining” Book, Bing Liu, 2007 “Opinion Mining and Sentiment Analysis” Book, Bo Pang and Lillian Lee, 2008
  • 27. What is Sentiment Classification?  Classify sentences/documents (e.g. reviews)/features based on the overall sentiments expressed by authors  positive, negative and (possibly) neutral  Similar to topic-based text classification  Topic-based classification: topic words are important  Sentiment classification: sentiment words are more important (e.g: great, excellent, horrible, bad, worst)
  • 28. A. Sentence Level Classification  Assumption: a sentence contains only one opinion (not true in many cases)  Task 1: identify if sentence is opinionated classes: objective and subjective (opinionated)  Task 2: determine polarity of sentence classes: positive, negative and neutral Sentiment Classification Quiz: “This is a beautiful bracelet..” Is this sentence subjective/objective? Is it positive, negative or neutral?
  • 29. Sentiment Classification B. Document(post/review) Level Classification  Assumption:  each document focuses on a single object (not true in many cases)  contains opinion from a single opinion holder (not true in many cases)  Task: determine overall sentiment orientation in document classes: positive, negative and neutral
  • 30. Sentiment Classification C. Feature Level Classification Goal: produce a feature-based opinion summary of multiple reviews  Task 1: Identify and extract object features that have been commented on by an opinion holder (e.g. “picture”,“battery life”).  Task 2: Determine polarity of opinions on features classes: positive, negative and neutral  Task 3: Group feature synonyms
  • 31. Example: Feature Level Classification – Camera Review
  • 32. Sentiment Classification  In summary, approaches used in sentiment classification  Unsupervised – eg: NLP pattern @ NLP patterns with lexicon  Supervised – eg: SVM, Naive Bayes..etc (with varying features like POS tags, word phrases)  Semi Supervised – eg: lexicon+classifier  Based on previous work, four features generally used a. Syntactic features b. Semantic features c. Link-based features d. Stylistic features  Semantic & Syntactic features are most commonly used
  • 33. Sentiment Classification Features Usually Considered A. Syntatic Features  What is syntactic feature? - Usage of principles and rules for constructing sentences in natural languages [wikipedia]  Different usage of syntactic features: POS+punctuation [Pang et al. 2002; Gamon 2004] POS Pattern [Nasukawa and Yi 2003; Yi et al. 2003; Fei et al. 2004; Wiebe et al 2004] Modifiers Whitelaw et al. [2005] >> POS (part-of-speech) tags & punctuation eg: a sentence containing an adjective and “!” could indicate existence of an opinion “the book is great !” >>POS n-gram patterns patterns like “n+aj” (noun followed by +ve adjective) - represents positive sentiment patterns like “n+dj” (noun followed by -ve adjective) - express negative sentiment >> Used a set of modifier features (e.g., very, mostly, not)  the presence of these features indicate the presence of appraisal “the book is not great” “..this camera is very handy”
  • 34. Sentiment Classification Features Usually Considered B. Semantic Features  Leverage meaning of words  Can be done manually/semi/fully automatically Score Based - Turney [2002] Lexicon Based - Whitelaw et al. [2005]  Use PMI calculation to compute the SO score for each word/phrase  Idea: If a phrase has better association with the word “Excellent” than with “Poor” it is positively oriented and vice versa Score computation: PMI (phrase ^ “excellent”) – PMI (phrase ^ “poor”) PMI- is a measure of association used in information theory. The PMI of a pair of x and y belonging to discrete random variables quantifies the discrepancy between the probability of their coincidence given their joint distribution versus the probability of their coincidence given only their individual distributions and assuming independence.  Use appraisal groups for assigning semantics to words/phrases  Each phrase/word is manually classified into various appraisal classes (eg: deny, endorse, affirm)
  • 35. Sentiment Classification Features Usually Considered C. Link-Based Features  Use link/citation analysis to determine sentiments of documents  Efron [2004] found that opinion Web pages heavily linking to each other often share similar sentiments  Not a popular approach D. Stylistic Features  Incorporate stylometric/authorship studies into sentiment classification  Style markers have been shown highly prevalent in Web discourse [Abbasi and Chen 2005; Zheng et al. 2006; Schler et al. 2006]  Ex. Study the blog authorship style of “Students vs Professors” Authorship Style of Students Authorship Style of Professors Colloquial@spoken style of writing Formal way of writing Improper punctuation Proper punctuation More usage of curse words & abbreviations Limited curse words & abbreviation
  • 36. Sentiment Classification – Recent Work Abbasi, Chen & Salem (TOIS-08)  Propose:  sentiment analysis of web forum opinions in multiple languages (English and Arabic)  Motivation:  Limited work on sentiment analysis on Web forums  Most studies have focused on sentiment classification of a single language  Almost no usage of stylistic feature categories  Little emphasis has been placed on feature reduction/selection techniques  New:  Usage of stylistic and syntactic features of English and Arabic  Introduced new feature selection algorithm: entropy weighted genetic algorithm (EWGA)  EWGA outperforms no feature selection baseline, GA and Information Gain  Results, using SVM indicate a high level of classification accuracy
  • 37. Sentiment Classification – Recent Work Abbasi, Chen & Salem (TOIS-08)
  • 38. Sentiment Classification – Recent Work Abbasi, Chen & Salem (TOIS-08)
  • 39. Sentiment Classification – Recent Work Abbasi, Chen & Salem (TOIS-08)
  • 40. Sentiment Classification – Recent Work Blitzer et al. (ACL 2007)  Propose:  Method for domain adaptation for sentiment classifiers (ML based) focusing on online reviews for different types of products  Motivation:  Sentiments are expressed differently in different domains - annotating corpora for every domain is impractical  If you train on the “kitchen” domain and classify on “book” domain  error increases  New:  Extend structural correspondence learning algorithm (SCL) to sentiment classification area  Key Idea:  If two topics/sentences from different domains have high correlation on unlabeled data, then we can tentatively align them  Achieved 46% improvement over a supervised baseline for sentiment classification
  • 41. Sentiment Classification – Recent Work Blitzer et al. (ACL 2007) • Do not buy the Shark portable steamer …. Trigger mechanism is defective. • the very nice lady assured me that I must have a defective set …. What a disappointment! • Maybe mine was defective …. The directions were unclear Unlabeled kitchen contexts • The book is so repetitive that I found myself yelling …. I will definitely not buy another. • A disappointment …. Ender was talked about for <#> pages altogether. • it’s unclear …. It’s repetitive and boring Unlabeled books contexts Aligning sentiments from different domains
  • 42. Sentiment Classification - Summary  Relatively focused & widely researched area  NLP groups  IR groups  Machine Learning groups (e.g., domain adaptation)  Important because:  With the wealth of information out on the web, we need an easy way to know what people think about a certain “topic” – e.g., products, political issues, etc  Heuristics generally used:  Occurrences of words  Phrase patterns  Punctuation  POS tags/POS n-gram patterns  Popularity of opinion pages  Authorship style
  • 43. Quiz Can you think of other heuristics to determine the polarity of subjective (opinionated) sentences?
  • 44. Opinion Retrieval  Is the task of retrieving documents according to topic and ranking them according to opinions about the topic  Important when you need people’s opinion on certain topic or need to make a decision, based on opinions from others General Search Opinion Search search for facts search for opinions/opinionated topics rank pages according to some authority and relevance scores Rank is based on relevance to topic and content of opinion
  • 45. Opinion Retrieval  “Opinion retrieval” started with the work of Hurst and Nigam (2004)  Key Idea: Fuse together topicality and polarity judgment  “opinion retrieval”  Motivation: To enable IR systems to select content based on a certain opinion about a certain topic  Method:  Topicality judgment: statistical machine learning classifier (Winnow)  Polarity judgment: shallow NLP techniques (lexicon based)  No notion of ranking strategy
  • 46. Opinion Retrieval Summary of TREC Blog Track (2006 – 2008) TREC 2006 Blog Track TREC 2007 Blog Track TREC 2008 Blog Track Opinion RetrievalOpinion Retrieval Same as 2006 with 2 new tasks: -blog distillation (feed search) -polarity determination Same as 2006 and 2007 with 1 new task: -Baseline blog post retrieval task (i.e. “Find me blog posts about X.”)
  • 47.
  • 48.  TREC-2006 Blog Track – Focus is on Opinion Retrieval  14 participants  Baseline System  A standard IR system without any opinion finding layer  Most participants use a 2 stage approach Opinion Retrieval Summary of TREC-2006 Blog Track [6] Ranked documents standard retrieval & ranking scheme Query opinion related re-ranking/filterRanked opinionated documents STAGE 1 STAGE 2 -tf*idf -language model -probabilistic -dictionary based -text classification -linguistics
  • 49. Opinion Retrieval Summary of TREC-2006 Blog Track [6]  TREC-2006 Blog Track  The two stage approach First stage  documents are ranked based on topical relevance  mostly off-the-shelf retrieval systems and weighting models  TF*IDF ranking scheme  language modeling approaches  probabilistic approaches. Second stage  results re-ranked or filtered by applying one or more heuristics for detecting opinions  Most approaches use linear combination of relevance score and opinion score to rank documents. eg: α and β are combination parameters
  • 50. Opinion Retrieval Summary of TREC-2006 Blog Track [6] Opinion detection approaches used:  Lexicon-based approach [2,3,4,5]: (a) Some used frequency of certain terms to rank documents (b) Some combined terms from (a) with information about the  distance between sentiment words &  occurrence of query words in the document Ex: Query: “Barack Obama” Sentiment Terms: great, good, perfect, terrific… Document: “Obama is a great leader….”  success of lexicon based approach varied ..of greatest quality………… ……nice……. wonderful…… …good battery life… ..of greatest quality………… ……nice……. wonderful…… …good battery life…
  • 51. Opinion Retrieval Summary of TREC-2006 Blog Track [6] Opinion detection approaches used:  Text classification approach:  training data:  sources known to contain opinionated content (eg: product reviews)  sources assumed to contain little opinionated content (eg:news, encyclopedia)  classifier preference: Support Vector Machines  Features (discussed in sentiment classification section):  n-grams of words– eg: beautiful/<ww>, the/worst, love/it  part-of-speech tags  Success of this approach was limited  Due to differences between training data and actual opinionated content in blog posts  Shallow linguistic approach:  frequency of pronouns (eg: I, you, she) or adjectives (eg: great, tall, nice) as indicators of opinionated content  success of this approach was also limited
  • 52. Opinion Retrieval Highlight: Gilad Mishne (TREC 2006) Gilad Mishne (TREC 2006)  Propose: multiple ranking strategies for opinion retrieval in blogs  Introduced 3 aspects to opinion retrieval  topical relevance  degree to which the post deals with the given topic  opinion expression  given a “topically-relevant” blog post, to what degree it contains subjective (opinionated) information about it  post quality  estimate of the quality of a “blog post”  assumption - higher-quality posts are likely to contain meaningful opinions
  • 53. Opinion Retrieval Highlight: Gilad Mishne (TREC 2006) Step 1: Is blog post Relevant to Topic? language modeling based retrieval language modeling based retrieval Ranked documents Ranked documents Query blind relevance feedback [9] blind relevance feedback [9] term proximity [10,11] term proximity [10,11] • add terms to original query by comparing language model of top- retrieved docs  entire collection • limited to 3 terms • every word n-gram from the query treated as a phrase temporal properties temporal properties • determine if query is looking for recent posts •boost scores of posts published close to time of the query date Topic relevance improvements Topic relevance improvements
  • 54. Opinion Retrieval Highlight: Gilad Mishne (TREC 2006) Step 2: Is blog post Opinionated?  Lexicon-based method- using GeneralInquirer  GeneralInquirer  large-scale, manually-constructed lexicon  assigns a wide range of categories to more than 10,000 English words  Example of word categories :  emotional category: pleasure, pain, feel, arousal, regret  pronoun category: self, our, and you; “The meaning of a word is its use in the language” - Ludwig Wittgenstein (1958)
  • 55. Opinion Retrieval Highlight: Gilad Mishne (TREC 2006) Step 2: Is blog post Opinionated? For each post calculate two sentiment related values known as “opinion level” Calculate opinion level Calculate opinion level Blog postBlog post Extract “topical sentences” from post to count the opinion-bearing words in it Topical sentences: >sentences relevant to topic >sentences immediately surrounding them “post opinion” level“post opinion” level “feed opinion” level“feed opinion” level (# of occurrences of words from any of “opinion indicating” categories ) total # of words Idea: Feeds containing a fair amount of opinions are more likely to express an opinion in any of its posts Method: > use entire feed to which the post belongs > topic-independent score per feed estimates the degree to which it contains opinions (about any topic)
  • 56. Opinion Retrieval Highlight: Gilad Mishne (TREC 2006) Step 3: Is the blog post of good quality?  A. Authority of blog post: Link-based Authority  Estimates authority of documents using analysis of the link structure  Key Idea:  placing a link to a page other than your own is like “recommending” that page  similar to document citation in the academic world  Follow Upstill et al (ADCS 2003) - inbound link degree (indegree) as an approximation  captures how many links there are to a page  Post’s authority estimation is based on:  Indegree of a post p & indegree of post p’s feed Site ASite A Site BSite B Site CSite C Blog Post P Blog Post P Authority=Log(indegree=3)
  • 57. Opinion Retrieval Highlight: Gilad Mishne (TREC 2006)] Step 3: Is the blog post of good quality?  B. Spam Likelihood  Method 1: machine-learning approach - SVM  Method 2: text-level compressibility - Ntoulas et al (WWW 2006)  Determine: How likely is post P from feed F a SPAM entry?  Intuition: Many spam blogs use “keyword stuffing”  High concentration of certain words  Words are repeated hundreds of times in the same post and across feed  When you detect spam post and compress them  high compression ratios for these feeds  Higher the compression ratio for feed F, more likely that post P is splog (Spam Blog) comp. ratio=(size of uncompressed pg.) / (size of compressed pg.) Final spam likelihood estimate: (SVM prediction) * (compressibility prediction)
  • 58. temporal properties temporal properties Opinion Retrieval Highlight: Gilad Mishne (TREC 2006) Step 4: Linear Model Combination top 1000 posts top 1000 posts 1.Topic relevance language model 1.Topic relevance language model blind relevance feedback [9] blind relevance feedback [9] term proximity query [10,11] term proximity query [10,11] 2.Opinion level2.Opinion level3.Post Quality3.Post Quality “feed opinion” level “feed opinion” level “post opinion” level “post opinion” level spam likelihood [13] spam likelihood [13] link based authority [12] link based authority [12] 4. Weighted linear combination of scores 4. Weighted linear combination of scores partial “post quality” scores partial “opinion level” scores ranked opinionated posts ranked opinionated posts final scores
  • 59. Opinion Retrieval Summary of TREC-2008 Blog Track  Opinion Retrieval & Sentiment Classification  Basic techniques are similar – classification vs. lexicon  More use of external information source  Traditional source: WordNet, SentiWordNet  New source: Wikipedia, Google search result, Amazon, Opinion web sites (Epinions.com, Rateitall.com)
  • 60. Opinion Retrieval Summary of TREC-2008 Blog Track  Retrieve ‘good’ blog posts 1. Expert search techniques  Limit search space by joining data by criteria  Used characteristics: number of comments, post length, the posting time -> estimate strength of association between a post and a blog. 1. Use of folksonomies  Folksonomy: collaborative tagging, social indexing.  User generating taxonomy  Creating and managing tagging.  Showed limited performance improvement
  • 61. Opinion Retrieval Summary of TREC-2008 Blog Track  Retrieve ‘good’ blog posts 3. Temporal evidence  Some investigated use of temporal span and temporal dispersion.  Recurring interest, new post. 3. Blog relevancy approach  Assumption:  A blog that has many relevant posts is more relevant.  The top N posts best represent the topic of the blog  Compute two scores to score a given blog.  The first score is the average score of all posts in the blog  The second score is the average score of the top N posts that have the highest relevance scores.  Topic relevance score of each post is calculated using a language modeling approach.
  • 62. Opinion Retrieval – Recent Work He et al (CIKM-08)  Motivation:  Current methods require manual effort or external resources for opinion detection  Propose:  Dictionary based statistical approach - automatically derive evidence of subjectivity  Automatic dictionary generation – remove too frequent or few terms with skewed query model  assign weights – how opinionated. divergence from randomness (DFR)  For term w, divergence D(opREl) from D(Rel) ( Retrieved Doc = Rel + nonRel. Rel = opRel + nonOpRel )  assign opinion score to each document using top weighted terms  Linear combine opinion score with initial relevance score  Results:  Significant improvement over best TREC baseline  Computationally inexpensive compared to NLP techniques
  • 63. Zhang and Ye (SIGIR 08)  Motivation:  Current ranking uses only linear combination of scores  Lack theoretical foundation and careful analysis  Too specific (like restricted to domain of blogs)  Propose:  Generation model that unifies topic-relevance and opinion generation by a quadratic combination  Relevance ranking serves as weighting factor to lexicon based sentiment ranking function  Different than the popular linear combination Opinion Retrieval – Recent Work
  • 64. Zhang and Ye (SIGIR 08)  Key Idea:  Traditional document generation model:  Given a query q, how well the document d “fits” the query q  estimate posterior probability p(d|q)  In this opinion retrieval model, new sentiment parameter, S (latent variable) is introduced Iop(d,q,s): given query q, what is the probability that document d generates a sentiment expression s  Tested on TREC Blog datasets – observed significant improvement Opinion Retrieval – Recent Work Opinion Generation Model Document Generation Model
  • 65. Challenges in opinion mining Summary of TREC Blog Track focus (2006 – 2008) TREC 2006 Blog Track TREC 2007 Blog Track TREC 2008 Blog Track Opinion RetrievalOpinion Retrieval Same as 2006 with 2 new tasks: -blog distillation (feed search) -polarity determination Same as 2006 and 2007 with 1 new task: -Baseline blog post retrieval task (i.e. “Find me blog posts about X.”) Main Lessons Learnt from TREC 2006, 2007 & 2008: Good performance in opinion-finding is strongly dependent on finding as many relevant documents as possible regardless of their opinionated nature
  • 66.  Many Opinion classification and retrieval system could not make improvements.  Used same relevant document retrieval model. Evaluate the performance of opinion module.  ΔMAP = Opinion finding MAP score with only retrieval system – Opinion finding MAP score with opinion module.  A lot of margins to research!!! Group ΔMAP of Mix ΔMAP of Positive ΔMAP of Negative KLE 4.86% 6.08% 3.51% UoGTr -3.77% -4.62% -2.76% UWaterlooEng -6.70% -1.69% -12.33% UIC_IR_Group -22.10% 2.12% -49.60% UTD_SLP_Lab -22.96% -17.51% -29.23% Fub -55.26% -59.81% -50.18% Tno -76.42% -75.93% -77.02% UniNE -43.68 -39.41% -48.49% Challenges in opinion mining Summary of TREC Blog Track focus (2006 – 2008)
  • 67. Challenges in opinion mining Highlight of TREC-2008 Blog Track Lee et al. Jia et al. (TREC 2008)  Propose:  Method for query dependent opinion retrieval and sentiment classification  Motivation:  Sentiments are expressed differently in different query. Similar to the Blitzer’s idea.  New:  Use external web source to obtain positive and negative opinionated lexicons.  Key Idea:  Objective words: Wikipedia, product specification part of Amazon.com  Subjective words: Reviews from Amazon.com, Rateitall.com and Epinions.com  Reviews rated 4 or 5 out of 5: positive words  Reviews rated 1 or 2 out of 5: negative words  Top ranked in Text Retrieval Conference.
  • 68. Challenges in opinion mining  Polarity terms are context sensitive.  Ex. Small can be good for ipod size, but can be bad for LCD monitor size.  Even in the same domain, use different words depending on target feature.  Ex. Long ‘ipod’ battery life vs. long ‘ipod’ loading time  Partially solved (query dependent sentiment classification)  Implicit and complex opinion expressions  Rhetoric expression, metaphor, double negation.  Ex. The food was like a stone.  Need both good IR and NLP techniques for opinion mining.  Cannot divide into pos/neg clearly  Not all opinions can be classified into two categories  Interpretation can be changed based on conditions.  Ex. 1) The battery life is ‘long’ if you do not use LCD a lot. (pos) 2) The battery life is ‘short’ if you use LCD a lot. (neg) Current system classify the first one as positive and second one as negative. However, actually both are saying the same fact.
  • 69. Opinion Retrieval – Summary  Opinion Retrieval is a fairly broad area (IR, sentiment classification, spam detection, opinion authority…etc)  Important:  Opinion search is different than general web search  Opinion retrieval techniques  Traditional IR model + Opinion filter/ranking layer (TREC 2006,2007,2008)  Some approaches in opinion ranking layer:  Sentiment: lexicon based, ML based, linguistics  Opinion authority - trustworthiness  Opinion spam likelihood  Expert search technique  Folksonomies  Opinion generation model  Unify topic-relevance and opinion generation into one model  Future approach:  Use opinion as a feature or a dimension of more refined and complex search tasks
  • 71. References  [1] M. Hurst and K. Nigam, “Retrieving topical sentiments from online document collections,” in Document Recognition and Retrieval XI, pp. 27–34, 2004.  [2] Liao, X., Cao, D., Tan, S., Liu, Y., Ding, G., and Cheng X.Combining Language Model with Sentiment Analysis for Opinion Retrieval of Blog-Post. Online Proceedings of Text Retrieval Conference (TREC) 2006. http://trec.nist.gov/  [3] Mishne, G. Multiple Ranking Strategies for Opinion Retrieval in Blogs. Online Proceedings of TREC, 2006.  [4] Oard, D., Elsayed, T., Wang, J., and Wu, Y. TREC-2006 at Maryland: Blog, Enterprise, Legal and QA Tracks. OnlineProceedings of TREC, 2006. http://trec.nist.gov/  [5] Yang, K., Yu, N., Valerio, A., Zhang, H. WIDIT in TREC-2006 Blog track. Online Proceedings of TREC, 2006. http://trec.nist.gov/  [6] Ounis, I., de Rijke, M., Macdonald, C., Mishne, G., and Soboroff, I. Overview of the TREC 2006 Blog Track. In Proceedings of TREC 2006, 15–27. http://trec.nist.gov/  [7] Min Zhang, Xingyao Ye: A generation model to unify topic relevance and lexicon-based sentiment for opinion retrieval. SIGIR 2008: 411-418  [9] J. M. Ponte. Language models for relevance feedback. In Advances in Information Retrieval: Recent Research from the Center for Intelligent Information Retrieval, 2000.  [10] D. Metzler and W. B. Croft. A markov random field model for term dependencies. In SIGIR ’05, 2005.  [11] G. Mishne and M. de Rijke. BoostingWeb Retrieval through Query Operations. In ECIR 2005, 2005.  [12] T. Upstill, N. Craswell, and D. Hawking. Predicting fame and fortune: Pagerank or indegree? In ADCS2003, 2003.  [13] A. Ntoulas, M. Najork, M. Manasse, and D. Fetterly. Detecting spam web pages through content analysis. In WWW 2006, 2006.  [14] An Effective Statistical Approach to Blog Post Opinion Retrieval. Ben He, Craig Macdonald Jiyin He, and Iadh Ounis. In Proceedings of CIKM 2008.
  • 72. References  [15] I. Ounis, C. Macdonald and I. Soboroff, Overview of the TREC 2008 Blog Track (notebook paper), TREC, 2008.  [16] Y. Lee, S.-H. Na, J. Kim, S.-H. Nam, H.-Y. Jung and J.-H. Lee , KLE at TREC 2008 Blog Track: Blog Post and Feed Retrieval (notebook paper), TREC, 2008.  [17] L. Jia, C. Yu and W. Zhang, UIC at TREC 208 Blog Track (notebook paper), TREC, 2008.

Editor's Notes

  1. Lets give this a slight twist… lets say the kid finished dinner and has gone to watch some TV.. My editing skills at work..