语料库研究中的主题词分析方法及其扩展ppt课件.pptx

语料库研究中的 主题词分the析keyw方orda a及chin其onr e n展saiolyns s o i t ppro 法 中国外语教育研究中心 梁茂成 主要内容 Keywords Applications of corpus comparison Limitations to the keyword approach Keywords+ Demo ☺Keywords are words whose frequency is unusually high (or low) in comparison with some norm. (Scott, 2003) Keywords ☻Keywords: 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 ☻Calculating keyness (Rayson et al. 2004, Oakes 1998) ☺ Chi-square Keywords Chi-square Keywords Chi-square with Yate’s correction tml References: http://ucrel.lancs.ac.uk/llwizard.h Keywords Loglikelihood 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 ☺ 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 ☺ …… Applicatons of… ☻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 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. Limitations to… Keywords+ ☻Support multiword