语料库研究中的主题词分析方法及其扩展.ppt

语料库研究中的 主题词分析方法及其扩展,中国外语教育研究中心 梁茂成,An extension to the keyword approach in corpus analysis,主要内容,Keywords Applications of corpus comparison Limitations to the keyword approach Keywords+ Demo,Keywords,Keywords: Keywords are words whose frequency is unusually high (or low) in comparison with some norm. (Scott, 2003),Keywords,Positive keywords: Words which occur more often than would be expected by chance in comparison with the reference corpus.,Keywords,Negative keywords: Words which occur less often than would be expected by chance in comparison with the reference corpus.,Keywords,Positive and negative keywords In a corpus of business English, words such as business, profit and companies are likely to be positive keywords if the corpus is to be compared with a general corpus.,Keywords,Positive and negative keywords In a corpus of academic English, words such as morning, afternoon and evening are likely to be negative keywords if the corpus is to be compared with a general corpus.,Keywords,Calculating keyness (Rayson et al. 2004, Oakes 1998) Chi-square,Keywords,Chi-square,Keywords,Chi-square with Yates correction,Keywords,Loglikelihood References: http:/ucrel.lancs.ac.uk/llwizard.html,Keywords,Previous research has revealed that loglikelihood is a better measure than chi-square when comparing word frequencies in corpora.,Keywords,Ways to find keywords: Top-down: corpus-based Buttom-up: corpus-driven,Applicatons of,Comparison across users Comparison across genres Comparison across times Comparison across (varieties of) languages,Applicatons of,Compiling a specialized dictionary Detecting the topic Genre analysis Contrastive Interlanguage Analysis ,Limitations to,Keywords: Do keywords have to be single words? Phraseology seems more interesting! Do keywords have to be lexical words? POS tag sequences may also be interesting. Can we bring together the bottom-up approach and the top-down approach?,Limitations to,Top-down: the problem is I do not yet know what may be interesting.,Limitations to,Buttom-up: the problem is that I have been given a long list of keywords, only some of which are interesting, buried among many others which do not seem interesting at all.,Keywords+,Su