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On Understanding and Classifying Web Queries. Prepared for :. Telcordia Contact: Steve Beitzel Applied Research steve@research.telcordia.com April 14, 2008. Overview. Introduction: Understanding Queries Query Log Analysis Automatic Query Classification Conclusions. Problem Statement.

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on understanding and classifying web queries

On Understanding and Classifying Web Queries

Prepared for:

Telcordia Contact:Steve Beitzel

Applied Research

steve@research.telcordia.com

April 14, 2008

overview
Overview
  • Introduction: Understanding Queries
  • Query Log Analysis
  • Automatic Query Classification
  • Conclusions
problem statement
Problem Statement
  • A query contains more information than just its terms
  • Search is not just about finding relevant documents – users have:
    • Target task (information, navigation, transaction)
    • Target topic (e.g., news, sports, entertainment)
    • General information need
  • User queries are simply an attempt to express all of the above in a couple of terms
problem statement 2
Problem Statement (2)
  • Current search systems focus mainly on the terms in the queries
  • Systems do not focus on extracting target task & topic information about user queries
  • We propose two techniques for improving understanding of queries
    • Large-Scale Query Log Analysis
    • Automatic Query Classification
  • This information can be used to improve general search effectiveness and efficiency
query log analysis
Query Log Analysis
  • Introduction to Query Log Analysis
  • Our Approach
  • Key Findings
  • Conclusions
introduction
Introduction
  • Web query logs are a source of information on users’ behaviors on the web
  • Analysis of logs’ contents may allow search services to better tailor their products to serve users’ needs
  • Existing query log analysis focuses on high-level, general measurements such as query length and frequency
our approach
Our Approach
  • Examine several aspects of the query stream over time:
    • Total query volume
    • Topical trends by category:
      • Popularity (Topical Coverage of the Query Stream)
      • Stability (Pearson Correlation of Frequencies)
query log characteristics
Query Log Characteristics
  • Analyzed two AOL search service logs:
    • One full week of queries from December, 2003
    • Six full months of queries; Sept. 2004-Feb. 2005
  • Some light pre-processing was done:
    • Case differences, punctuation, & special operators removed; whitespace trimmed
  • Basic statistics:
    • Queries average 2.2 terms in length
    • Only one page of results is viewed 81% of the time
    • Two pages: 18%
    • Three or more: 1%
category breakdown
Category Breakdown
  • Query lists for each category formed by a team of human editors
  • Query stream classified by exactly matching each query to category lists
key findings
Key Findings
  • Some topical categories vary substantially more in popularity than others over an average day
    • Some topics are more popular during particular times of the day
    • others have a more constant level of interest
  • Most Individual categories are substantially less divergent over longer periods
    • Still some seasonal changes (Sports, Holidays)
key findings1
Key Findings
  • The query sets for different categories have differing similarity over time
    • The level of similarity between the actual query sets received within topical categories varies differently according to category
  • As we move out to very large time scales, new trends become apparent:
    • Climatic (Seasonal)
    • Holidays
    • Sports-related
  • Several major events fall within the studied six-month period, causing high divergence in some categories
  • Long-term trends like these can potentially be very useful for query routing & disambiguation
summary
Summary
  • Query Stream contains trends that are independent of volume fluctuation
  • Query Stream exhibits different trends depending on the timescale being examined
  • Future work may be able to leverage these trends for improvement in areas such as
    • Caching strategies
    • Query disambiguation
    • Query routing & classification
automatic query classification
Automatic Query Classification
  • Introduction: Query Classification
  • Motivations & Prior Work
  • Our approach
  • Results & Analysis
  • Conclusions
  • Future Work
introduction1
Introduction
  • Goal is to conceive an approach that can identify a query with relevant topical categories
  • Automatic classifiers help a search service decide when to use specialized databases
  • Specialized databases may provide tailored, topic-specific results
problem statement1
Problem Statement
  • Current search systems focus mainly on the terms in the queries
  • No focus on extracting topic information
  • Manual query classification is expensive
  • Does not take advantage of the large supply of unlabeled data available in query logs
prior work
Prior Work
  • Much early text classification was document-based
  • Query Classification:
    • Manual (human assessors)
    • Automatic
      • Clustering Techniques – doesn’t help identify topics
      • Supervised learning via retrieved documents
        • Still expensive – retrieved documents must be classified
automatic query classification motivations
Automatic Query Classification Motivations
  • Web queries have very few features
  • Achieving and sustaining classification recall is difficult
  • Web query logs provide a rich source of unlabeled data; we must harness these data to aid classification
our approach1
Our Approach
  • Combine three methods of classification:
    • Labeled Data Approaches:
      • Manual (exact-match lookup using labeled queries)
      • Supervised Learning (Perceptron trained with labeled queries)
    • Unlabeled Data Approach:
      • Unsupervised Rule Learning with unlabeled data from a large query log
    • Disjunctive Combination of the above
approach 1 exact match to manual classifications
Approach #1 - Exact-Match to Manual Classifications
  • A team of editors manually classified approximately 1M popular queries into 18 topical categories
    • General topics (sports, health, entertainment)
    • Mostly popular queries
  • Pros
    • Expect high precision from exact-match lookup
  • Cons
    • Expensive to maintain
    • Very low classification recall
    • Not robust to changes in the query stream
approach 2 supervised learning with a perceptron
Approach #2 - Supervised Learning with a Perceptron
  • Goal: achieve higher levels of recall than human efforts
  • Supervised Learning
    • Used heavily in text classification
      • Bayes, Perceptron, SVM, etc…
    • Use manually classified queries to train a classifier
  • Pros:
    • Leverages available manual classifications for training
    • Finds features that are good predictors of a class
  • Cons:
    • Entirely dependant on the quality andquantity of manual classifications
    • Does not leverage unlabeled data
approach 3 unsupervised rule learning using unlabeled data
Approach #3 - Unsupervised Rule Learning Using Unlabeled Data
  • We have query logs with very large numbers of queries
    • Must take advantage of millions of users showing us how they look for things
    • Build on manual efforts
  • Manual efforts tell us some words from each category
    • Find words associated with each category
    • Learn how people look for topics, e.g. “what words do users use to find musicians or lawn-mowers”
unsupervised rule learning using unlabeled data 2
Unsupervised Rule Learning Using Unlabeled Data (2)
  • Find good predictors of a class based on how users look for queries related to certain categories
  • Use those words to predict new members of each category
  • Apply the notion of selectional preferences to find weighted rules for classifying queries automatically
selectional preferences step 1
Selectional Preferences: Step 1
  • Obtain a large log of unlabeled web queries
  • View each query as pairs of lexical units:
    • <head, tail>
    • Only applicable to queries of 2+ terms
    • Queries with n terms form n-1 pairs
    • Example: “directions to DIMACS” forms two pairs:
      • <directions, to DIMACS> and <directions to, DIMACS>
  • Count and record the frequency of each pair
selectional preferences step 2
Selectional Preferences: Step 2
  • Obtain a set of manually labeled queries
  • Check the heads and tails of each pair to see if they appear in the manually labeled set
  • Convert each <head, tail> pair into:
    • <head, CATEGORY> (forward preference)
    • <CATEGORY, tail> (backward preference)
    • Discard <head, tail> pairs for which there is no category information at all
    • Sum counts for all contributing pairs and normalize by the number of contributing pairs
selectional preferences step 3
Selectional Preferences: Step 3
  • Score each preference using Resnik’s Selectional Preference Strength formula:
  • Where urepresents a category, as found in Step 2.
  • S(x) is the sum of the weighted scores for every category associated with a given lexical unit
selectional preferences step 4
Selectional Preferences: Step 4
  • Use the mined preferences and weighted scores from Steps 3 and 4 to assign classifications to unseen queries
selectional preference rule examples
Forward Rules

harlem club X

ENT->0.722

PLACES->0.378

TRAVEL->1.531

harley all stainless X

AUTOS->3.448

SHOPPING->0.021

harley chicks with X

PORN->5.681

Backward Rules

X gets hot wont start

AUTOS->2.049

PLACES->0.594

X getaway bargain

PLACES->0.877

SHOPPING->0.047

TRAVEL->0.862

X getaway bargain hotel and airfare

PLACES->0.594

TRAVEL->2.057

Selectional Preference Rule Examples
combined approach
Combined Approach
  • Each approach exploits different qualities of our query stream
  • A natural next step is to combine them
    • How similar are the approaches?
evaluation metrics
Evaluation Metrics
  • Classification Precision:
    • #true positives / (#true positives + #false positives)
  • Classification Recall:
    • #true positives / (#true positives + # false negatives)
  • F-Measure:

Higher values of beta put more emphasis on recall

experimental data sets
Experimental Data Sets
  • Separate collections for training and testing:
    • Training:
      • Nearly 1M web queries manually classified by a team of editors
      • Grouped non-exclusively into 18 topical categories, and trained each category independently
      • Query log of several hundred million queries used for forming SP rules
    • Testing:
      • 20,000 web queries classified by human assessors
      • ~30% agreement with classifications in training set
      • 25% of the testing set was set aside for tuning the perceptron & SP classifiers
kdd cup 2005
KDD Cup 2005
  • 2005 KDD Cup task was Query Classification
  • 800,000 queries and 67 topical categories
  • 800 queries judged by three assessors
  • Top performers used information from retrieved documents
    • Retrieved result snippets for aiding classification decisions
    • Top terms from snippets and documents used for query expansion
  • Systems evaluated on precision and F1
kdd cup experiments
KDD Cup Experiments
  • We mapped our manual classifications on to the KDD cup category set
    • Obviously an imperfect mapping
      • Our categories are general, i.e. “Sports”
      • KDD Cup categories are specific, i.e. “Sports-Baseball”
    • Running a retrieval pass is prohibitively expensive
      • We relied only on our general manual classifications and queries in the log
conclusions
Conclusions
  • Our system successfully makes use of large amounts of unlabeled data
  • The Selectional Preference rules allow us to classify a significantly larger portion of the query stream than manual efforts alone
  • Excellent potential for further improvements
future work
Future Work
  • Expand available classification features per query
    • Mine web query logs for related terms and patterns
  • More intelligent combination methods
    • Learned combination functions
    • Voting algorithms
  • Utilize external sources of information
    • Patterns and trends from query log analysis
    • Topical ontology lookups
  • Use automatic query classification to improve effectiveness and efficiency in a production search system
related bibliography
Related Bibliography
  • Journals
    • S. Beitzel, et. al, “Temporal Analysis of a Very Large Topically Categorized Query Log”, Journal of the American Society for Information Science and Technology (JASIST), Vol. 58, No. 2, 2007.
    • S. Beitzel, et. al, “Automatic Classification of Web Queries Using Very Large Unlabeled Query Logs”, ACM Transactions on Information Systems (TOIS), Vol. 25, No. 2, April 2007.
  • Conferences
    • S. Beitzel, et. al, “Hourly Analysis of a Very Large Topically Categorized Web Query Log", ACM-SIGIR, July 2004.
    • S. Beitzel, et. al “Automatic Query Classification”, ACM-SIGIR, August 2005.
    • S. Beitzel, et. al, “Improving Automatic Query Classification via Semi-supervised Learning”, IEEE-ICDM, November 2005.
questions
Questions?
  • Thanks!