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翻訳と辞書　辞書検索 [ 開発暫定版 ] スポンサード リンク Conjunctive grammar ： ウィキペディア英語版 Conjunctive grammar Conjunctive grammars are a class of formal grammars studied in formal language theory. They extend the basic type of grammars, the context-free grammars, with a conjunction operation. Besides explicit conjunction, conjunctive grammars allow implicit disjunction represented by multiple rules for a single nonterminal symbol, which is the only logical connective expressible in context-free grammars. Conjunction can be used, in particular, to specify intersection of languages. A further extension of conjunctive grammars known as Boolean grammars additionally allows explicit negation. The rules of a conjunctive grammar are of the form :$A\; \backslash to\; \backslash alpha\_1\; \backslash And\; \backslash ldots\; \backslash And\; \backslash alpha\_m$ where $A$ is a nonterminal and $\backslash alpha\_1$, ..., $\backslash alpha\_m$ are strings formed of symbols in $\backslash Sigma$ and $N$ (finite sets of terminal and nonterminal symbols respectively). Informally, such a rule asserts that every string $w$ over $\backslash Sigma$ that satisfies each of the syntactical conditions represented by $\backslash alpha\_1$, ..., $\backslash alpha\_m$ therefore satisfies the condition defined by $A$. Two equivalent formal definitions of the language specified by a conjunctive grammar exist. One definition is based upon representing the grammar as a system of language equations with union, intersection and concatenation and considering its least solution. The other definition generalizes Chomsky's generative definition of the context-free grammars using rewriting of terms over conjunction and concatenation. Though the expressive means of conjunctive grammars are greater than those of context-free grammars, conjunctive grammars retain some practically useful properties of the latter. Most importantly, there are generalizations of the main context-free parsing algorithms, including the linear-time recursive descent, the cubic-time generalized LR, the cubic-time Cocke-Kasami-Younger, as well as Valiant's algorithm running as fast as matrix multiplication. A number of theoretical properties of conjunctive grammars have been researched, including the expressive power of grammars over a one-letter alphabet and numerous undecidable decision problems. This work provided a basis for the study language equations of a more general form. ==References == * Alexander Okhotin, ''Conjunctive grammars.'' Journal of Automata, Languages and Combinatorics, 6:4 (2001), 519-535. ((pdf) ) * Alexander Okhotin, ''An overview of conjunctive grammars.'' In: Gheorghe Paun, Grzegorz Rozenberg, Arto Salomaa (Eds.), Current Trends in Theoretical Computer Science: The Challenge of the New Century, Vol. 2, World Scientific, 2004, 545--566. ((pdf) ) * Artur Jeż. ''Conjunctive grammars can generate non-regular unary languages.'' International Journal of Foundations of Computer Science 19(3): 597-615 (2008) (Technical report version (pdf) ) 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Conjunctive grammar」の詳細全文を読む スポンサード リンク 翻訳と辞書 : 翻訳のためのインターネットリソース Copyright(C) kotoba.ne.jp 1997-2016. All Rights Reserved.