A Web-based Question Answering System

Yu-shan & Wenxiu

03.08.2005

Outline

• System Architecture

• Query Expansion

• Pattern Learning

• Answering Extraction

• Performance & Evaluation

Our QA

• Massive web documents based

– how to eliminate noise…

• Question classification

– Focus on LOC

– (LOC:city, LOC:country, LOC:state, LOC:other…)

• Multiple Query Expansion

• Suffix tree to aid surface pattern learning

• Use Regular Expression to extract answer

System Architecture

Question Expansion

• No expansion• Delete question words & stop words

– Save more space for expansion

• WordNet Synonym Expansion– Word ambiguous

• Dependency-based Word Similarity Expansion– Prof. Lin@Univ. of Alberta – http://www.cs.ualberta.ca/~lindek/demos/depsim.htm

Question Expansion Example

• Question:– What is the largest city in the world?

• Primary keywords:– is largest city world

• WordNet expansion:– is largest city world be metropolis human race

• Similarity expansion:– is largest city world doing town region

Suffix Tree

• Construct a general suffix tree for the top 100 snippets– each node has an index of the sentences it appears.– Set threshold N, pick up the longest common

substrings which appear in more than N sentence, use them as candidate answers.

– Manually filtering correct candidate answers to construct patterns

• Huge Noise…– Query keywds, common words, part of phrases…– Laborious manual work…

LOC:city Patterns

• <NAME> is <ANS>• <ANS> is <NAME>• <ANS>, <NAME>• <NAME>, <ANS>• <NAME>, ….., is <ANS>• <ANS>, ……, is <NAME>• <NAME>, ……, <ANS>• <ANS>,……, <NAME>• <ANS> <NAME>• <NAME> <ANS>

Answer Extraction

• Regular Expression Match

• Known_city_list filtering…– Contains 4682 cities…

• Direct pick out citynames from snippet

• Combine two approaches

• DEMO TIME

Answers from Google

• What is the largest city in the world?• TREC answer: Tokyo• Our answer:

– Seoul– Memphis– Tokyo– Mexico City– Los Angeles

Google snippet:“With a population of more than 10.2 million, Seoul, the capital of

South Korea, is the world?s largest city in terms of population.”“…… we see that Memphis remained the largest city in the world

from at least 3100 BCE to 2240 BCE”

Evaluation

• Use TREC-10 Labeled Questions

ORIG PRIM WN SIM

MRR 0.75 0.6 0.47 0.52

PropCorrect

0.8 0.8 0.6 0.5