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 Context-free grammar - Wikipedia, the free encyclopedia
For instance, given a context-free grammar, one can use the Chomsky Normal Form to construct a polynomial-time algorithm which decides whether a given string is in the language represented by that grammar or not (the CYK algorithm).
Context-free grammars are powerful enough to describe the syntax of most programming languages; in fact, the syntax of most programming languages are specified using context-free grammars.
On the other hand, context-free grammars are simple enough to allow the construction of efficient parsing algorithms which, for a given string, determine whether and how it can be generated from the grammar. /wiki/Context-free_grammar   (1310 words)

 PlanetMath: context-free language
A context-free grammar is a grammar that generates a context-free language.
Context-free grammars are also known as Type-2 grammars in the Chomsky hierarchy.
Backus-Naur Form (or BNF as it is commonly denoted) is a convenient notation used to represent context-free grammars in a much more intuitive manner than the definition above. /encyclopedia/ContextFreeGrammar.html   (440 words)

 Diagrams: a context free grammar
This is an example of an encoding of a context free grammar. /software/thistle/demos/cfg.html   (12 words)

 Context-Free Grammars
Grammar designers should keep this list to a minimum because the efficiency of the grammar -- both the processing required and the accuracy of recognition -- can be affected by the number of exported rules.
If an application loads another grammar that exports a rule of that name, the first grammar borrows that rule and all of the vocabulary referenced by the rule from the second grammar, even if the second grammar is not activated.
When grammars are linked, one grammar indicates that it imports a rule from another grammar and identifies the rule name by a string. /ttshelp/contxtFree.html   (1203 words)

 S-attributed context-free grammars
S-attributed context-free grammars, which are a proper subset of attributed-grammars introduced by Knuth in his seminal paper [
An ambiguous grammar is a grammar for which there exists a string of symbols having at least two different derivation trees.
As previously noted, grammars used for biological sequence analysis are ambiguous because they aim at describing the space of all possible configurations. /Labo/Jerome.Waldispuhl/tutorial/node1.html   (479 words)

 The Omphalos Context-Free Grammar Learning Competition
For each target grammar a set of positive sentences were constructed, such that for every rule in the target grammar, a positive sentence was added to the training set that is derived using that rule.
According to Lemma 8 where the grammar is known to be deterministic this implies that a set of candidate grammars can be constructed from the training set that includes the target grammar.
The most specific grammar can be represented by a grammar, where for each node of all derivation trees, that non-terminal is not used in any derivation tree. /Omphalos/generation2.html   (3740 words)

 ECML/PKDD 2003 Workshop: Context-Free Grammar Learning
Yet long term dependencies, palindromic structures, parenthesis are all internal structures that may appear in a wide range of applications and are better described by context free grammars.
In this field researchers are beginning to turn their attention to induction of context-free grammars.
An area that is of vital importance in this context is grammar induction. /~mvzaanen/ECMLPKDD/workshop.html   (974 words)

 Recitation 5 Notes
Give a context free grammar that generates the language of all strings with an equal number of zeros and ones.
Give a context free grammar that generates the language of all strings that contain 101.
Give a context free grammar that generates the complement of the language 0*1*. /~dimitrik/aduni_stuff/2090/theory/recit5.html   (189 words)

 To prove Context Free Grammar (CFG) is LL1
To prove your CFG (Context Free Grammar) is LL1 or not.
I was tired of proving the CFG is LL1 or not, so I wrote this program to do the tedious and time-consuming job.
In my CS510 (Compiler Design) course, we were asked to write CFG for a sample language (subset of C), and later write syntax analyzer for it. /~zyllh/cs510/ll1.htm   (401 words)
For any context-free grammar that does not ;;; generate the null string, there is a context-free grammar in Chomsky;;; normal form that generates exactly the same strings.
The algorithm ;;; presented here converts an arbitrary context-free grammar into one that ;;; is in Chomsky normal form by progressively reducing the variety of the ;;; rules.
(define add-unique-start-symbol (lambda (cfg) (let ((old-start (context-free-grammar-start-symbol cfg))) (let ((new-start (gensym))) (make-context-free-grammar (context-free-grammar-terminals cfg) (cons new-start (context-free-grammar-non-terminals cfg)) (cons (make-rule new-start (list old-start)) (context-free-grammar-rules cfg)) new-start))))) ;;; The GENSYM procedure constructs and returns a non-terminal of a form ;;; that is unlikely to have been used in the grammar. /~stone/courses/linguistics/   (1009 words)

 Context-Free Grammars
A context-free grammar is a set of recursive rewriting rules (or productions) used to generate patterns of strings.
Context-free grammars are often used to define the syntax of programming languages.
A parse tree displays the structure used by a grammar to generate an input string. /u/leblanc/csc173/grammars   (132 words)

 Context Free
A context free grammar is a description of a language in a set of rules.
Context Free lets you write a set of rules about how to generate an image, and then follows those rules to create a image.
The process is considered context free because each expansion of a symbol via some rule can be done independently of any of the expansions of other symbols. /ContextFree/about.html   (609 words)

 Probabilistic Context Free Grammars
It generates the same set of parses for a text that the corresponding context free grammar does, and assigns a probability to each parse.
Probabilistic context free grammars are implemented by the
) is a context free grammar that associates a probability with each of its productions. /tutorial/pcfg/section-pcfg.html   (291 words)

 Context-Free Grammars
Given a grammar G with start symbol S, if there is some sequence of productions that, when applied to the initial string S, result in the string s, then s is in L(G), the language of the grammar.
We can prove that this grammar generates the language by induction on n, the number of zeros and ones in the string.
We can define a grammar G for which there there is no FA F such that L(F) == L(G). /u/leblanc/csc173/grammars/cfg.html   (1474 words)

 Context Free
Context Free is copyright © 2005 Mark Lentczner and John Horigan.
It's free, as in beer and as in speech.
These grammars are sets of non-deterministic rules to produce images. /ContextFree   (170 words)

 Context Free Grammar
The context free grammar represents the syntax of a language.
A CFG is used to describe the ways symbols (tokens) can be combined to form legal sentences in a language.
SALLAD (So Another Lousy Language And Diagrams) CFG /benjamin_plessing/cfg.html   (62 words)

Grammar is the study of the rules governing the use of a language.
The formal study of grammar is an important part of education from a young age through advanced learning, though the rules taught in schools are not a "grammar" in the sense most linguists use the term, as they are often prescriptive rather than descriptive.
Grammar is part of the general study of language called linguistics. /grammar.html   (744 words)

 Stochastic context-free grammar -- Facts, Info, and Encyclopedia article
SCFGs extend context-free grammars in the same way that (additional info and facts about hidden Markov model) hidden Markov models extend (additional info and facts about regular grammar) regular grammars.
This is equivalent to the probability of the SCFG generating the sequence, and is intuitively a measure of how consistent the sequence is with the given grammar.
The probability of a derivation (parse) is then the product of the probabilities of the productions used in that derivation; thus some derivations are more consistent with the stochastic grammar than others. /encyclopedia/S/St/Stochastic_context-free_grammar.htm   (686 words)

 Language defined by a context free grammar
Language defined by a context free grammar The set of all string of terminal symbols derivable from the start symbol. /~tingue/cogsci1/site/section03/subsection9/main.html   (20 words)

 Parser Tools in Prolog
As an example of a context-free grammar, here is a specification of the context-free grammar for arithmetic expression.
The specification of the contex-free grammar for a language consists of four items, the specification of the terminal symbols of the language, the specification of the nonterminals, the productions or derivation rules, and the start symbol of the grammar.
A grammar is LL(1) (suitable for top-down parsing with one symbol of look ahead) iff it satisfies the following two rules. /~aabyan/464/ParserTools.html   (808 words)

 W&B Scientific - Context-Free Grammar Considered Harmful
Context-free grammar and Markov models, while natural in theory, have not until recently been considered essential.
Lee, I. Newton, J. Quinlan, D. Patterson, F. Corbato, and J. Anderson, "Context-free grammar considered harmful," University of Washington, Tech.
Along these same lines, we place our work in context with the prior work in this area [3]. /Miscellaneous/71/Context-Free-Grammar-Considered-Harmful.html   (2182 words)

 Transformations on Context Free Grammars
unification grammars as every context free grammar is a unification grammar (without any change or syntactic manipulation).
Note that parsers for context free grammars can be generated with the package
converts a BNF back into the usual format with grammar rules and lexicon entries. /mogul/doc/niehren/context-free-grammar   (106 words)

 W&B Scientific - Construction of Context-Free Grammar
The flaw of this type of solution, however, is that context-free grammar and semaphores are regularly incompatible.
Hawking, "Comparing digital-to-analog converters and context-free grammar with mosk," Journal of Linear-Time Symmetries, vol.
We place our work in context with the existing work in this area. /Miscellaneous/81352/Construction-of-Context-Free-Grammar.html   (1529 words)

 Context-Free Grammar --- Part I
The concept of context-free grammar and of derivability in grammar are introduced.
The notion convenient to prove facts on language generated by grammar with exchange of symbols on grammar of union and concatenation of languages is included.
Moreover, the language (set of finite sequences of symbols) generated by grammar and some grammars are defined. /JFM/Vol4/lang1.html   (101 words)

 Example of Structured Context-Free Grammar, cont.
The patterns generated for the example grammar are: /bjornw/doc/yggdrasil/yggdrasil-9.html   (8 words)

 Program Files\Netscape\Communicator\Program\UAExp\CFGs
Context-free grammars where originally developed by Noam Chomsky as a means for describing the underlying syntax (grammar) of natural languages.
Despite this fact, context-free grammars are still very useful and reflect the underlying algebraic structure of both kinds of languages.
We will later give an example of a programming language, the language LANG1, that does have a context-free grammar. /~wagner/UASCR/CFGs.htm   (663 words)

 an introduction to poetry rhythm and rhythmic analysis
Free verse originated in France around the middle of the nineteenth century, was championed (briefly) by the founders of Modernism, and has ramified into various forms, some of them indistinguishable from prose.
Free verse is the form most widely used in contemporary poetry, but is anything but new.
Free verse is very confused field, not properly understood or linguistically mapped. /advanced/rhythm.html   (663 words)

 BioMed Central Full text Evaluation of several lightweight stochastic context-free grammars for RNA secondary structure prediction
Although one implementation of an SCFG mirror of the Zuker algorithm has been described [35], it used a structurally ambiguous grammar (it was not intended for secondary structure prediction per se; it was only used in summed Inside algorithm calculations where ambiguity doesn't matter, not in a CYK algorithm where ambiguity does matter).
It can be tricky to write grammars that are structurally unambiguous, and it appears to be difficult to prove that they are so, except in simple cases.
Once stacking correlations are included, four of the grammars (G6, G7, G8, and G6) have comparably good performance, at the cost of increasing parameter number to include the 16 × 16 parameters set for the three with stacking correlations. /1471-2105/5/71   (7989 words)

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