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Searching with Context

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Presentation on theme: "Searching with Context"— Presentation transcript:

1 Searching with Context
Reiner Kraft Farzin Maghoul Chi Chao Chang Ravi Kumar Yahoo!, Inc., Sunnyvale, CA 94089, USA

2 Evaluation and Results Conclusion
Agenda Motivation Contextual Search Introduction Case Study: Y!Q Algorithms Query Rewriting Rank-Biasing Iterative, Filtering Meta-search (IFM) Evaluation and Results Conclusion

3 Motivation Traditional web search based on keywords as good as it gets? Not too much qualitative differences between search results of major search engines Introducing anchor text and link analysis to improve search relevancy last major significant feature (1998) Search can be vastly improved in the dimension of precision The more we know about a user’s information need, the more precise our results can be There exists a lot of evidence (context) beyond the terms in the query box from which we can infer better knowledge of information need Study of web query logs show that users are already employing a manual form of contextual search by using additional terms to refine and reissue queries when the search results for the initial query turn out to be unsatisfactory => How can we automatically use context for augmenting, refining, and improving a user’s search query to obtain more relevant results?

4 Contextual Search - General Problems
Gathering evidence (context) Representing and inferring user information need from evidence Using that representation to get more precise results

5 Contextual Search - Terminology
In general: Any additional information associated with a query More narrow: A piece of text (e.g., a few words, a sentence, a paragraph, an article) that has been authored by someone Context Term Vector Dense representation of a context in the vector space model Obtained using keyword extraction algorithms (e.g., Wen-tau Yih et al., KEA, Y! Content Analysis) Search Query Types Simple: Few keywords, no special or expensive operators Complex: Keywords/phrases plus special ranking operators, more expensive to evaluate Contextual: Query + context term vector Search Engine Types Standard: Web search engines (e.g., Yahoo, Google, MSN, …) that support simple queries Modified: A Web search engine that has been modified to support complex search queries

6 Case Study: Y!Q Contextual Search
Acquiring context: Y!Q provides a simple API that allows publishers to associate visual information widgets (actuators) to parts of page content (http://yq.search.yahoo.com/publisher/embed.html) Y!Q lets users manually specify or select context (e.g., within Y! Toolbar, Y! Messenger, included JavaScript library) Contextual Search Application Generates a digest (context term vector) of the associated content piece as additional terms of interest for augmenting queries (content analysis) Knows how to perform contextual searches for different search back-end providers (query rewriting framework) Knows how to rank results based on query + context (contextual ranking) Seamless integration by displaying results in overlay or embedded within page without interrupting the user’s workflow

7 Example

8 Example Y!Q Actuator

9 Example Y!Q Overlay showing contextual search results

10 Example Add csrp Y!Q: Searching in Context

11 Example CSRP Terms extracted from context

12 Y!Q System Architecture

13 Implementing Contextual Search
Assumption: We have a query plus a context term vector (contextual search query) Design dimensions: Number of queries to send to a search engine per contextual search query Types of queries to send Simple Complex Algorithms: Query Rewriting (QR) Rank-Biasing (RB) Iterative, Filtering, Meta-Search (IFM)

14

15 Algorithm 1: Query Rewriting
Combine query + context term vector using AND/OR semantics Input Parameters: Query, context term vector Number of terms to consider from context term vector Experimental Setup: QR1 (takes top term only) QR2 (takes top two terms only) … up to QR5 Example: QR3: Given query q and => q AND a AND b AND c Pros: Simplicity, supported in all major search engines Cons: Possibly low recall for longer queries

16 Algorithm 2: Rank-Biasing
Requires modified search engine with support for RANK operator for rank-biasing Complex query comprises: Selection part Optional ranking terms are only impacting score of selected documents Input Parameters: Query, context term vector Number of selection terms to consider (conjunctive semantics) Number of RANK operators Weight multiplier for each RANK operator (used for scaling) Experimental Setup: RB2 (uses 1 selection term, 2 RANK operators, weight multiplier=0.1) RB6 (uses 2 selection terms, 6 RANK operators, weight multiplier=0.01) Example: RB2: Given q and => q AND a RANK(b, 2.5) RANK(c, 1.2) Pros: Ranking terms do not limit recall Cons: Requires a modified search engine back-end, more expensive to evaluate

17 Algorithm 3: IFM IFM based on concept of Meta-search (e.g., used in Buying Guide Finder [kraft, stata, 2003]) Sends multiple (simple) queries to possibly multiple search engines Combines results using rank aggregation methodologies

18 IFM Query Generation Uses “query templates” approach: Parameters:
Query templates specify how sub-queries get constructed from the pool of candidate terms Allow to explore the problem domain in a systematic way Implemented primarily sliding window technique using query templates Example: Given query q and => a sliding window query template of size 2 may construct the following queries: q a b q b c q c d Parameters: Size of the sliding window Experimental Setup: IFM-SW1, IFM-SW2, IFM-SW3, IFM-SW4

19 IFM uses Rank Aggregation for combining different result sets
Rank aggregation represents a robust and principled approach of combining several ranked lists into a single ranked list Given universe U, and k ranked lists 1, …, k on the elements of the universe Combine k lists into *, such that is minimized For d(.,.) we used various distance functions (e.g,. Spearman footrule, Kendall tau) Parameters: Style of rank aggregation: Rank averaging (adaptation of Borda voting method) MC4 (based on Markov chains,more computationally expensive) Experimental Setup: IFM-RA, IFM-MC4

20 Experimental Setup and Methodology
Benchmark 200 contexts sampled from Y!Q query logs Tested 41 configurations 15 QR (Yahoo, MSN, Google) 18 RB (1 or 2 selection terms; 2, 4, or 6 RANK operators, 0.01, 0.1, or 0.5 weight multipliers) 8 IFM (avg and MC4 on Yahoo, SW1 to SW4) Per item test Relevancy to the context, perceived relevancy used Relevancy Judgments: Yes Somewhat No Can’t Tell 28 expert judges, look at top 3 results, total of 24,556 judgments

21 Example Context: Judgment Examples:
“Cowboys Cut Carter; Testaverde to Start OXNARD, Calif Quincy Carter was cut by the Dallas Cowboys on Wednesday, leaving 40-year-old Vinny Testaverde as the starting quarterback. The team would’nt say why it released Carter.” Judgment Examples: A result directly relating to the “Dallas Coyboys” (football team) or Quincy Carter => Yes A result repeating the same or similar information => Somewhat A result about Jimmy Carter, the former U.S. president => No If result doesn’t provide sufficient information => Can’t tell

22 Metrics Strong Precision at 1 (SP@1) and 3 (SP@3)
Number of relevant results divided by the number of retrieved results, but capped at 1 or 3, and expressed as a ratio A result is considered relevant if and only if it receives a ‘Y’ relevant judgment Precision at 1 and 3 A result is considered relevant if and only if it receives a ‘Y’ or ‘S’ relevant judgment

23 Coverage Results Highlights
Substantial drop in recall as number of vector entries in QR increases (expected), comparable between MSN, Yahoo, roughly one order of magnitude less on Google For QR4 using MSN, Yahoo, low recall may potentially affect user experience RB configurations tested same recall as QR2 IFM works on substantially larger set of candidate results

24 Relevance Results for QR
Highlights Use metrics SP drops sharply for MSN, Yahoo beyond QR4 (recall issues) Optimal operating point for MSN, Yahoo QR3/QR4, Google QR5 QR4 uses 7.3 terms avg., QR5 uses 8.51 terms avg.

25 Relevance Results for RB and IFM
Highlights RB2/RB6 best configurations within RBs, RB2 has highest IFM-RA-SW3 winner (best

26 Discussion of Results Simple QR can attain high relevancy
However, precision decreases as function of low recall Optimal setting depends on web search engine Human reformulations are unlikely to attain the same level of relevancy as that of QR (best QR1 issues 2.25 terms attains of 0.504) RB can perform competitively particularly at Additional experiments showed that some good results are bubbling up from middle-tier of results (ranked between positions 100 and 1000) Does not do well for (problem if the “right” results are not recalled by selection part) Requires substantial modifications to a web search engine Contextual search is not solely a ranking problem, but one of recall IFM achieves highest recall and overall relevancy Can be competitive and, in some measures, superior to QR More costly to execute

27 Conclusion Investigated three algorithmsd for implementing contextual search: QR RB IFM can be easily implemented on top of a commodity search engine Performs surprisingly well Likely to be superior to manual query reformulation Recall problems RB and IFM break recall limitations of QR IFM very effective Outperforms both QR and RB in terms of recall and precision The three algorithms offer a good design spectrum for contextual search implementers

28 Future Work Further tuning of contextual search algorithms Alterative presentations of context Improve relevancy of context term vectors Better word sense disambiguation Investigate the usage of different context types (e.g., time, location, user profiles) Improve contextual ranking and blending of different source types How to leverage semantic web technologies

29 Interested? Email your resume to: thinkbig@yahoo-inc.com

30 Backup Slides

31 Example Search Scenarios
User wants to find the nearest movie theater Context: location Query: “movie theater” User reads a press article about the new Mac OS X Tiger and wants to learn more about it Context: news article Query: review User signs in to Yahoo! and wants to plan trip to ‘Java’ Context: search history, user preferences Query: java => Query alone not sufficient! => Context critical for returning relevant results => Users often manually append context in form of adding extra query terms Users often append context in form of query terms to query


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