课件跨语言讯检索导论.ppt

Selection Strategy: Select All(Continued) Davis 1997 (TREC5) Replace each English query term with all of its Spanish equivalent terms from the Collins bilingual dictionary. Monolingual (0.2895) vs. All-equivalent substitution (0.1422): 49.12% Hsin-Hsi Chen * Evaluation Method Average Precision (5-, 9-, 11-points) Model Spanish Query Mono IR Engine English Query Bilingual Dictionary Mono IR Engine TREC Spanish Corpus Spanish Equivalents English Query Mono IR Engine TREC Spanish Corpus Spanish Equivalents by POS POS Bilingual Dictionary TREC Spanish Corpus Hsin-Hsi Chen * Selection Strategy: Select N Simple word-by-word translation Each query term is replaced by the word or group of words given for the first sense of the term’s definition. 50-60% drop in performance (average precision) Hsin-Hsi Chen * Selection Strategy: Select N(Continued) word/phrase translation Take at most three translations of each word, one from each of the first three senses. Take phrase translation if appearing in dictionary. 30-50% worse than good translation Well-translated phrases can greatly improve effectiveness, but poorly translated phrases may negate the improvements. WBW (0.0244), phrasal (0.0148), good phrasal (0.0610) -39.3% +150.3% Hsin-Hsi Chen * Selection Strategy: Select Best N Hayashi, Kikui and Susaki 1997 search for a dictionary entry corresponding to the longest sequence of words from left to right choose the most frequently used word (or phrases) in a text corpus collected from WWW no report for this query translation approach Davis 1997 (TREC5) POS disambiguation Monolingual (0.2895) vs. All-equivalent substitution (0.1422) vs. POS disambiguation (0.1949): near 67.3% Hsin-Hsi Chen * Corpus-Based Approaches Categorization Term-Aligned Sentence-Aligned Document-Aligned (Parallel, Comparable) Unaligned Usage Setup Thesaurus Vector Mapping Hsin-Hsi Chen * Term-Aligned Corpora Fine-grained alignment in parall