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Context-Free Grammars for English

Context-Free Grammars for English. 인공지능 연구실 허 희 근. Contents. Introduce What is a CFG (Context-Free Grammar) Context-Free Rules and Trees Sentence-Level Constructions The Noun Phrase Coordination Agreement The Verb Phrase and Subcategorization. Introduce(1).

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Context-Free Grammars for English

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  1. Context-Free Grammars for English 인공지능 연구실 허 희 근 Context-Free Grammars for English

  2. Contents • Introduce • What is a CFG (Context-Free Grammar) • Context-Free Rules and Trees • Sentence-Level Constructions • The Noun Phrase • Coordination • Agreement • The Verb Phrase and Subcategorization Context-Free Grammars for English

  3. Introduce(1) • Introduce a number of more complex notion of syntax and grammar. • Three main new ideas • Constituency : 단일 unit 또는 phrase를 가지는 word group • Ex) noun pharse • Grammatical relations : SUBJECTS와 OBJECTS에 대한 전통문법 형식화 • Ex) She ate a mammoth breakfast. • she (SUBJECT), a mammoth breakfast (OBJECT) • Subcategorization and dependencies : words와 phrase사이의 relation Context-Free Grammars for English

  4. Introduce(2) • Introduce the use of Context-Free Grammars. • All of these kinds of syntactic knowledge can be modeled by various kinds of grammars that are based on CFG. • CFG are backbone of many models of the syntax of natural language (of computer languages). • Powerful enough to express sophisticated relations among the words in a sentence. • CFG are integral to most models of natural language understanding, of grammar checking. Context-Free Grammars for English

  5. What is a CFG (Context-Free Grammar) (1) • 영문에서 문장은 phrase가 모여 이루어진 것이므로 문장의 구조를 명확히 하기 위해서는 구의 구성을 아는 것이 기본이라는 것으로 출발 • 문장의 처음부터 끝까지 rewriting rule을 적용함으로써 그 문장을 표현하는 parse tree를 구성해 나가는 것 Context-Free Grammars for English

  6. What is a CFG (Context-Free Grammar) (2) • Rewriting rule • 이러한 법칙을 문장의 처음부터 끝까지 적용하여 tree를 만듦 (a) S NP·VP·PP (b) VP V·NP (c) NP DET·N (d) NP N (e) PP PREP·NP (f) N boy, window, hammer (g) DET the, a (h) V broke (i) PREP with Context-Free Grammars for English

  7. What is a CFG (Context-Free Grammar) (3) • CFG parse tree (The boy broke the window with a hammer.) Context-Free Grammars for English

  8. Context-Free Rules and Trees(1) • CFG는 일반적으로 영문이나 다른 자연어에서 그것을 구성하는 구조를 모델화할 때 가장 많이 쓰이는 수학적 시스템 • CFG는 rules 또는 productions 의 set을 구성 • 이것들은 Language symbols이 그룹화하고 순서를 정할 수 있는 방법을 표현 • Symbols는 CFG가 두 개의 클래스로 나눌 때 사용 • Terminal symbols : word에 해당하는 symbols (“the”, “nightclub”) • Non-terminals : terminal symbols의 clusters 또는 generalization을 표현하는 symbols Context-Free Grammars for English

  9. Context-Free Rules and Trees(2) • CFG는 보통 두 가지의 방법으로 생각함 • 문장을 일반화 시키기 위한 방법 • 주어진 문장의 구조의 정하기 위한 방법 • Generator : (arrow) • Rewrite the symbol on the left with the string of symbols on the right. • CFG는 랜덤하게 연속된 string을 일반화시킬 때 사용 • This sequence of rule expansions is called a derivation of the string of words. • Represent a derivation by a parse tree Context-Free Grammars for English

  10. Context-Free Rules and Trees(3) Sample lexicon Grammar rule Context-Free Grammars for English

  11. Context-Free Rules and Trees(3) Parse tree Context-Free Grammars for English

  12. Sentence-Level Constructions • There are a great number of possible overall sentence structures. • But four are particularly common and important. • Declarative structure • Imperative structure • Yes-no-question structure • Wh-question structure Context-Free Grammars for English

  13. The Noun Phrase(1) • The syntax of English allows for both prenominal (pre-head) modifiers and post-nominal (post-head) modifiers. • Before the Head Noun • Noun phrases can begin with a determiner • Ex) a stop, the flights, that fare, this flight, those flights… • Noun이 복수형일 때는 determiner 생략할 수 있음 • Predeterminers : word class appear in the NP before the determiner. • Common predeterminer is all • Ex) all the flights, all flight • Word class appear in the NP between the determiner and the head noun. • Cardinal numbers, ordinal numbers, quantifiers • rule of prenominal modifiers • NP (Det) (Card) (Ord) (Quant) (AP) Nominal Context-Free Grammars for English

  14. The Noun Phrase(2) • After the Noun • A head noun can be followed by postmodifiers. • Prepositional phrases, relative clauses • brackets inserted to show the boundaries of each PP. • Ex) a reservation [on flight six oh six] [form Tampa] [to Montreal] • Nominal Nominal PP (PP) (PP) Context-Free Grammars for English

  15. Coordination • Noun phrases and other units can be conjoined with conjunctions like and, or, and but. • NP NP and NP • VP VP and VP • S S and S Context-Free Grammars for English

  16. Agreement • Rule of 3sg subjects and non-3sg subjects • S Aux NP VP S 3sgAux 3sgNP VP S Non3sgAux Non3sgNP VP • 3SgNP (Det) (Card) (Ord) (Quant) (AP) SgNominal • Non3SgNP (Det) (Card) (Ord) (Quant) (AP) PlNominal 3sgAux : does | has | can | … Non3sgAux : do | have | can | … Context-Free Grammars for English

  17. The Verb Phrase and Subcategorization Some subcategorization frames and example verbs Context-Free Grammars for English

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