Huizhong Doan, Yonbo Cao, Chin-Yew Lin and Yong Yu
Shanghai Jiao Tong University & MSRA
ACL 2008
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Question & their Answers
 A very large archives
 Built up by
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Example
 Traditional FAQ services
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Q&A services
▪ Emerging
▪ Yahoo! Answers, Live QnA, Baidu Zhidao
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Question Search
Help users to search previous answers
Any nice hotels in Berlin or Hamburg?
How long does it take to Hamburg from Berlin?
Cheap hotels in Berlin?
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Identifying question topic & focus
 Question tree
 Determining the tree cut
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Modeling question topic & focus for search
 Language model
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Topic terms
 BaseNP, WH-ngram
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Topic profile
 probability distribution of categories
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Specificity
 inverse of the entropy of the topic profile
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Topic chain
 topic terms ordered by specificity value (desc)
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Topic tree
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M=(Γ,θ)
 Γ = [ C1, C2, .. Ck ] , tree cut
 Θ = [ P(C1), P(C2), .. P(Ck) ] , prob param vector
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A cut is any set of nodes
Σi=1..kP( Ci ) = 1
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[n0, n11], [n12, n21, n22, n23], [n13, n24]
[n11, n21, n22, n23, n24]
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Minimum Description Length
Ref : Li and Abe, 1998
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P( q | q )
 q : queried question
~
 q : targeted question
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Yahoo! Answers
Resolved questions
 travel : 314,616 items
 computers & internet : 210,785 items
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Tree fields
 title ( only used )
 description
 answers
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Employed Vector Space Model
Manual judgments : relevant / irrelevant
Baseline : VSM, LMIR
Evaluation : MAP, R-precision, MRR
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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 )
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(a) explains why λ is 0.7
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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 best
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Lexical chasm
 Where to stay in Hamburg?
 The best hotel in Hamburg?
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IBM model 1
 Use question titles and question description as the
parallel corpus
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1)
2)
3)
4)
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Data Structure
Use MDL-based Tree Cut Model to Identify
A new form of language modeling for
question search
Extensive experiments
Now only community-based
From forum sites / FAQ sites
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