Slide 1Slide 2Slide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11A Web-based Question Answering SystemYu-shan & Wenxiu03.08.2005Outline•System Architecture•Query Expansion•Pattern Learning•Answering Extraction•Performance & EvaluationOur 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 answerSystem ArchitectureQuestion 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.htmQuestion 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 regionSuffix 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 TIMEAnswers from Google•What is the largest city in the world?•TREC answer: Tokyo•Our answer: –Seoul–Memphis–Tokyo–Mexico City–Los AngelesGoogle 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 QuestionsORIG PRIM WN SIMMRR 0.75 0.6 0.47 0.52PropCorrect 0.8 0.8 0.6
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