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摘要:6.7Modeling Linguistic Patterns 建模语言模式 Classifiers can help us to understand the linguistic patterns that occur in natural language, by allowing us to create explicit models that capture those patterns. Typically, these models are using supervised classification techniques, but it is also possible . 阅读全文
posted @ 2011-09-03 18:27 牛皮糖NewPtone 阅读 (722) 评论 (0) 编辑
摘要:6.6Maximum Entropy Classifiers最大熵分类器 The Maximum Entropy classifier uses a model that is very similar to the model employed by the naive Bayes classifier. But rather than using probabilities to set the model's parameters, it uses search techniques to find a set of parameters that will maximize t 阅读全文
posted @ 2011-09-03 18:25 牛皮糖NewPtone 阅读 (5176) 评论 (0) 编辑
摘要:6.5Naive Bayes Classifiers朴素贝叶斯分类器 In naive Bayes classifiers, every feature gets a say in determining which label should be assigned to a given input value. To choose a label for an input value, the naive Bayes classifier begins by calculating the prior probability(先验概率) of each label, which is de. 阅读全文
posted @ 2011-09-03 18:21 牛皮糖NewPtone 阅读 (3810) 评论 (0) 编辑
摘要:6.4Decision Trees 决策树 In the next three sections, we'll take a closer look at three machine learning methods that can be used to automatically build classification models: decision trees, naive Bayes classifiers, and Maximum Entropy classifiers. As we've seen, it's possible to treat thes 阅读全文
posted @ 2011-09-03 18:13 牛皮糖NewPtone 阅读 (3253) 评论 (0) 编辑
摘要:6.3Evaluation 评分 In order to decide whether a classification model is accurately capturing a pattern, we must evaluate that model. The result of this evaluation is important for deciding how trustworthy the model is, and for what purposes we can use it. Evaluation can also be an effective tool for . 阅读全文
posted @ 2011-09-01 21:57 牛皮糖NewPtone 阅读 (1089) 评论 (0) 编辑
摘要:6.2Further Examples of Supervised Classification 监督式分类的更多例子 Sentence Segmentation 句子分割 Sentence segmentation can be viewed as a classification task for punctuation: whenever we encounter a symbol that could possibly end a sentence, such as a period or a question mark, we have to decide whether it .. 阅读全文
posted @ 2011-08-31 23:16 牛皮糖NewPtone 阅读 (1119) 评论 (0) 编辑
摘要:Chapter6 Learning to Classify Text学习文本分类 Detecting patternsis a central part of Natural Language Processing(模式检测是自然语言处理的核心内容). Words ending in -ed tend to be past tense verbs (Chapter 5). Frequent use of will is indicative of news text (Chapter 3). These observable patterns — word structure and wo.. 阅读全文
posted @ 2011-08-31 14:13 牛皮糖NewPtone 阅读 (2375) 评论 (0) 编辑
摘要:5.10Exercises 练习 ☼ Search the web for "spoof newspaper headlines", to find such gems as: British Left Waffles on Falkland Islands, and Juvenile Court to Try Shooting Defendant. Manually tag these headlines to see if knowledge of the part-of-speech tags removes the ambiguity. ☼... 阅读全文
posted @ 2011-08-30 22:51 牛皮糖NewPtone 阅读 (1270) 评论 (0) 编辑
摘要:5.9Further Reading 深入阅读 Extra materials for this chapter are posted at http://www.nltk.org/, including links to freely available resources on the web. For more examples of tagging with NLTK, please see the Tagging HOWTO at http://www.nltk.org/howto. Chapters 4 and 5 of (Jurafsky & Martin, 2008) 阅读全文
posted @ 2011-08-30 22:49 牛皮糖NewPtone 阅读 (324) 评论 (0) 编辑
摘要:5.8Summary小结 • Words can be grouped into classes, such as nouns, verbs, adjectives, and adverbs. These classes are known as lexical categories or parts-of-speech. Parts-of-speech are assigned short labels, or tags, such as NN and VB. 单词可以分成类,例如名词,动词,形容词以及副词。这些类被称为词汇类别或者词性。词性被赋给了短标签或者标记,例如NN或者VB。... 阅读全文
posted @ 2011-08-30 22:46 牛皮糖NewPtone 阅读 (387) 评论 (0) 编辑
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