Rick Liu 1

Huizhong Doan, Yonbo Cao, Chin-Yew Lin and Yong YuShanghai Jiao Tong University & MSRA

ACL 2008

Searching Question by Identifying Question Topic and Question Focus

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Introduction

Question & their Answers A very large archives Built up by Online Services

Example Traditional FAQ services Community-based Q&A services▪ Emerging▪ Yahoo! Answers, Live QnA, Baidu Zhidao

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Motivation

Question Search Help users to search previous

answers

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Any cool clubs in Berlin or Hamburg?

What are the best/most fun clubs in Berlin? Any nice hotels in Berlin or Hamburg? How long does it take to Hamburg from

Berlin? Cheap hotels in Berlin?

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Motivation

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Any cool clubs in Berlin or Hamburg?

Question TopicQuestion Focus

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Approach

Identifying question topic & focus Question tree Determining the tree cut

Modeling question topic & focus for search Language model

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Question Tree

Topic terms BaseNP, WH-ngram

Topic profile probability distribution of categories

Specificity inverse of the entropy of the topic profile

Topic chain topic terms ordered by specificity value

(desc) Topic tree2008/7/9

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Question Tree Example

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Tree Cut Model

M = ( Γ , θ ) Γ = [ C1, C2, .. Ck ] , tree cut Θ = [ P(C1), P(C2), .. P(Ck) ] , prob

param vector A cut is any set of nodes Σi=1..kP( Ci ) = 1

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Tree Cut Model Example

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[n0, n11], [n12, n21, n22, n23], [n13, n24][n11, n21, n22,

n23, n24]

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MDL-base Tree Cut Model

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Minimum Description Length

Ref : Li and Abe, 1998

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Determining the Tree Cut

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HEADTAIL

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Modeling for Search

P( q | q ) q : queried question q : targeted question

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~

~

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Experimental Data

Yahoo! Answers Resolved questions

travel : 314,616 items computers & internet : 210,785 items

Tree fields title ( only used ) description answers

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Ground Truth

Employed Vector Space Model Manual judgments : relevant /

irrelevant

Baseline : VSM, LMIR Evaluation : MAP, R-precision, MRR

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Results for ‘travel’

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Results for ‘computer & internet’

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About the λ

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Emphasize more in question topic

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Error Analysis ( travel )

Examine the correctness of question topics and question foci

200 queried question => 69 question incorrect (a) Only have the head part ( 59 ) (b) Incorrect order ( 10 )

(a) explains why λ is 0.7

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Related Work

FAQ data Community based

Jeon et al., 2005 Compared four different retrieval

methods▪ Vector space model▪ Okapi▪ Language model▪ Translation-based model

Translation-based model performed the best2008/7/9

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Translation Model

Lexical chasm Where to stay in Hamburg? The best hotel in Hamburg?

IBM model 1 Use question titles and question

description as the parallel corpus

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Results

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Conclusions and Future Work

1) Data Structure2) Use MDL-based Tree Cut Model to

Identify3) A new form of language modeling

for question search4) Extensive experiments

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Now only community-based From forum sites / FAQ sites

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Thanks

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Modeling for Search

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Translation Probability

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