.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 主要内容 Keywords Keywords Keywords Keywords Keywords Keywords Keywords Keywords Keywords Keywords Keywords Applicatons of… Applicatons of… Limitations to… Limitations to… Limitations to… Keywords+ Demo 中国外语教育研究中心 梁茂成 An extension tothe keyword approach in corpus analysis Keywords Applications of corpus comparison Limitations to the keyword approach Keywords+ Demo Keywords: Keywords are words whose frequency is unusually high (or low) in comparison with some norm. (Scott, 2003) Positive keywords: Words which occur more often than would be expected by chance in comparison with the reference corpus. Negative keywords: Words which occur less often than would be expected by chance in comparison with the reference corpus. 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. 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. Calculating keyness (Rayson et al. 2004, Oakes 1998) Chi-square Chi-square Chi-square with Yate’s correction Loglikelihood References: http://ucrel.lancs.ac.uk/llwizard.html Previous research has revealed that loglikelihood is a better measure than chi-square when comparing word frequencies in corpora. Ways to find keywords: Top-down: corpus-based Buttom-up: corpus-driven Comparison across users Comparison across genres Comparison across times Comparison across (varieties of) languages Compiling a specialized dictionary Detecting the topic Genre analysis Contrastive Interlanguage Analysis …… 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? Top-down: the prob