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xử lý ngôn ngữ tự nhiên,kai wei chang,www cs virginia edu Lecture 14 Formal Grammars Kai Wei Chang CS @ University of Virginia kw@kwchang net Couse webpage http //kwchang net/teaching/NLP16 1CS6501 NL[.]

Lecture 14: Formal Grammars Kai-Wei Chang CS @ University of Virginia kw@kwchang.net Couse webpage: http://kwchang.net/teaching/NLP16 CS6501: NLP CuuDuongThanCong.com https://fb.com/tailieudientucntt Critical review report (due 10/20) v page maximum v Pick one paper from the suggested list v Summarize the paper (use you own words) v Provide detailed comments v What can be improved v Potential future directions v Other related work v Example (see reviewer at: https://goo.gl/yrBXXo) CS6501– Natural Language Processing CuuDuongThanCong.com https://fb.com/tailieudientucntt How to model language? v So far, all the models we saw formulate sentence as a sequence v Language models v POS-tagging v Morphological analysis CS6501: NLP CuuDuongThanCong.com https://fb.com/tailieudientucntt Next key concepts v In the following few weeks, we will go beyond sequence models v Syntactic parsing – model language as a recursive generating process v Often use a tree structure CS6501: NLP CuuDuongThanCong.com https://fb.com/tailieudientucntt What is grammar? v A compact way to define and describe the structure of sentences v Why we need grammar? v Number of C++ programs? C++ standard (2014) 976 pages ISO/IEC 14882:2014 1358 pages CS6501: NLP CuuDuongThanCong.com https://fb.com/tailieudientucntt Can we define a program that generates all English sentences? CS6501: NLP CuuDuongThanCong.com From Julia Hockenmaier, Intro to NLP https://fb.com/tailieudientucntt Basic sentence structure CS6501: NLP CuuDuongThanCong.com https://fb.com/tailieudientucntt A Markov Model v I eat shshi; I eat meat; you eat banana… v Great, it covers many sentences CS6501: NLP CuuDuongThanCong.com https://fb.com/tailieudientucntt Words take different arguments v [Good] I eat sushi v [Bad] I sleep sushi v [Bad] I give sushi v Intransitive verbs (sleep): no object v Transitive verbs (eat): take one direct object v Ditransitive verbs (give): take an additional indirect object CS6501: NLP CuuDuongThanCong.com https://fb.com/tailieudientucntt A better model CS6501: NLP CuuDuongThanCong.com 10 https://fb.com/tailieudientucntt Constituency v Groups of words that behave as a single unit or phrase v E.g., Noun phrases: the man, a girl with glasses v Prepositional phrases: with classes, on a table v Verb phrase: eat sushi, sleep, sleep soundly v Phrases has a head: v Other parts called dependents v E.g, the man, a girl with glasses CS6501: NLP CuuDuongThanCong.com 17 https://fb.com/tailieudientucntt Properties of constituents v Substitution v He talks [in class] ⇒ He talks [there] v It can move around in a sentence v He talks [in class] ⇒ [In class], he talks v Can be used as an answer: v Where does he talk? – [In class] CS6501: NLP CuuDuongThanCong.com 18 https://fb.com/tailieudientucntt Types of dependencies v Phrases has a head: v Other parts called dependents v E.g, the man, a girl with glasses v Dependents can be arguments or adjuncts v Arguments are obligatory v E.g., [John] likes [Mary] v Adjuncts are optional v E.g., John runs [fast] v Adverbs, PPs, Adjectives… All arguments have to be present and cannot be occupied multiple times Can be an arbitrary number of adjuncts CS6501: NLP CuuDuongThanCong.com 19 https://fb.com/tailieudientucntt How to represent the structure CS6501: NLP CuuDuongThanCong.com 20 https://fb.com/tailieudientucntt ... 976 pages ISO/IEC 14882:2014 1358 pages CS6 501: NLP CuuDuongThanCong.com https://fb.com/tailieudientucntt Can we define a program that generates all English sentences? CS6 501: NLP CuuDuongThanCong.com... sentence structure CS6 501: NLP CuuDuongThanCong.com https://fb.com/tailieudientucntt A Markov Model v I eat shshi; I eat meat; you eat banana… v Great, it covers many sentences CS6 501: NLP CuuDuongThanCong.com... Ditransitive verbs (give): take an additional indirect object CS6 501: NLP CuuDuongThanCong.com https://fb.com/tailieudientucntt A better model CS6 501: NLP CuuDuongThanCong.com 10 https://fb.com/tailieudientucntt

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