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Topic: Context free grammars


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In the News (Tue 23 Jul 19)

  
 Introduction
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.
The purpose of the workshop is to provide a forum specific to this question, enabling researchers to present their most recent results over the issue of learning context-free grammars.
In this field researchers are beginning to turn their attention to induction of context-free grammars.
ilk.uvt.nl /~mvzaanen/ECMLPKDD/introduction.html

  
 Grammar Inference using Evolutionary-Based Techniques
We are interested in the development of evolutionary-based techniques for the generation of grammars of different kinds (particularly regular and context-free) from a finite set of positive and negative examples.
Julio César Sandria Reynoso is currently working in the induction of context-free grammars using genetic algorithms, to characterize sequences of symbols.
These representation schemes should allow the generation of regular and context-free grammars in a compact form as to allow the use of reasonably small strings to represent relatively complex grammars.
www.lania.mx /~ccoello/grammar.html   (829 words)

  
 PlanetMath: 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.
The syntaxes of most programming languages are context-free grammars (or very close to it).
planetmath.org /encyclopedia/ContextFreeGrammar.html   (440 words)

  
 27-tk-abs.txt
In this paper we restrict ourselves to stochastic context-free grammars which, while more analytically tractable than our SNet grammars, are more difficult than others previously considered by the GA community.
Our GA introduces a novel encoding of grammars as genotypic strings, and uses a local search component to aid in learning rule probabilities.
We give results for two grammars whose nonstochastic equivalents have been used in previous studies.
www.cs.ucsd.edu /~rik/foga4/Abstracts/27-tk-abs.txt   (146 words)

  
 Information and Control -- 1975
Generalizations of regular sets and their applicatin to a study of context-free languages.
On the syntactic structures of unrestricted grammars I. generative grammars and phrase structure grammars.
The characterization by automata of certain classes of languages in the context sensititve area.
theory.lcs.mit.edu /~iandc/ic75.html   (340 words)

  
 Context-free grammar - Wikipedia, the free encyclopedia
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.
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).
en.wikipedia.org /wiki/Context-free_grammar   (1310 words)

  
 Context Free
Hence, Context Free, an environment for editing and rendering CFDG design grammars.
Context Free is copyright © 2005 Mark Lentczner and John Horigan.
It's free, as in beer and as in speech.
www.ozonehouse.com /ContextFree   (170 words)

  
 Michael Paul Stewart Brown Publications
Stochastic context-free grammars (SCFGs) are applied to the problems of folding, aligning and modeling families of tRNA sequences.
A model based on intersections of stochastic context free grammars is presented to allow for the modeling of RNA pseudoknot structures.
This work presents the theory and application of stochastic context-free grammars (SCFGs) to biological sequence analysis and specifically to the problem of RNA secondary structure modeling.
www.soe.ucsc.edu /%7Empbrown/mpsbPapers/index.html   (1677 words)

  
 Information and Control -- 1971
Complexity and unambiguity of context-free grammars and languages.
A few remarks on the index of context-free grammars and languages.
The generative capacity of transformational grammars of Ginsburg and Partee.
theory.lcs.mit.edu /~iandc/ic71.html   (330 words)

  
 Simon Lucas - 1994 - Structuring Chromosomes for Context-free Grammar Evolution
Abstract This paper investigates the use of genetic algorithms for inferring small regular and context­free grammars.
However, the application of grammars is limited by the algorithms we can apply to infer them from samples of data.
An example of this may be seen in speech recognition, where hidden Markov models (equival­ ent to stochastic regular grammars) are applied with great success.
www.isrl.uiuc.edu /~amag/langev/paper/lucas94structuringChromosomes.html   (367 words)

  
 Research Questions in Grammar Specialisation and Disambiguation
For instance, it is quite possible to envision stochastic context-free grammars of lexical dependency structures in which each of the non-terminal nodes in the stochastic context-free grammar relates to a word in the input sentence.
Note, however, that the lack of expressiveness with respect to lexical dependencies is not an inherent property of stochastic context-free grammars, but rather a property of their typical use.
In stochastic context-free grammars, grammar rules are augmented with probabilities.
odur.let.rug.nl /~vannoord/alp/proposal/node16.html   (1024 words)

  
 Citations: Decidability of bisimulation equivalence for processes generating context-free languages - Baeten, Bergstra, Klop (ResearchIndex)
Context free languages are accepted by both context free grammars, and pushdown automata.
BPA (Basic Process Algebra) stands for the class of infinite state processes, associated with normalform context free grammars, where only left most derivation is allowed 1.
Context free rewriting systems have been used for description and analysis for several classes of infinite state systems such as BPA and pushdown processes (e.g.
citeseer.csail.mit.edu /context/33832/0   (1024 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.
ilk.uvt.nl /~mvzaanen/ECMLPKDD/workshop.html   (974 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.
www.ozonehouse.com /ContextFree   (170 words)

  
 Mildly context sensitive grammar formalisms
Summary: While there is conclusive proof that not all natural languages can be described by context-free grammars, all available evidence suggests that a very cautious extension of this complexity class is sufficient to accommodate all linguistic phenomena.
Friday: Linear context-free rewriting systems, Minimalist Grammars, example of a minimalist grammar
An introduction to mildly context sensitive grammar formalisms
www.ling.uni-potsdam.de /~jaeger/esslli2004   (170 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.
SCFGs are used to model the patterns in (additional info and facts about RNA gene) RNA gene families in the Rfam Database, and search genome sequences for likely additional members of these families.
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.
www.absoluteastronomy.com /encyclopedia/S/St/Stochastic_context-free_grammar.htm   (686 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.
www.ii.uib.no /~wagner/UASCR/CFGs.htm   (663 words)

  
 Program Files\Netscape\Communicator\Program\UAExp\CFGs
Despite this fact, context-free grammars are still very useful and reflect the underlying algebraic structure of both kinds of languages.
Context-free grammars where originally developed by Noam Chomsky as a means for describing the underlying syntax (grammar) of natural languages.
We will later give an example of a programming language, the language LANG1, that does have a context-free grammar.
www.ii.uib.no /~wagner/UASCR/CFGs.htm   (663 words)

  
 hitaka.html
This means that for an inconsistent grammar, the expected applied number of a rewriting rule is not proportionate to the true value of the parameter attached to the rule, so it is hard to come up with a consistent parameter estimation for {inconsistent} stochastic context free grammars.
Stochastic Context Free Grammars are widely used as a convenient probabilistic language model for speech recognition.
We concentrated our research mainly on the characterization of { consistency} (or {inconsistency}) of stochastic context free grammar this year and solved almost all problems related to the subject.
winnie.kuis.kyoto-u.ac.jp /taiwa/e-abst94/hitaka.html   (442 words)

  
 Computational Theory and Formal Languages - Languages of type 2 - context-free and Push-down Automata
Example: A context-free grammar is specified by the sets: N={S,A,B}, T={a,b},S is the start symbol, the rules R are defined as below:
If Lis a non-empty context-free language, it can be generated by a context-free grammar G with the following properties:
Relations between LR(k) grammar and Push-down Automata are given in Table 11 In Tables 12 oraz 13 are given examples of LR(k) grammars with k=1 and k=3.
wuwuwu.com.pl /jf/teo7-e.htm   (1264 words)

  
 LINGUIST List 14.1254: Phonology/Morphology; Computational Ling
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.
The purpose of the workshop is to provide a forum specific to this question, enabling researchers to present their most recent results over the issue of learning context-free grammars.
All paper presenters will be provided free accomodation for up to four nights in a centrally located hotel.
www.ling.ed.ac.uk /linguist/issues/14/14-1254.html   (574 words)

  
 Stochastic Context-Free Grammars, stochastic languages
The estimation of stochastic context-free grammars using the Inside-Outside algorithm.
Moments of strings and derivation lengths of stochastic context-free grammars.
A trellis-based algorithm for estimating the parameters of a hidden stochastic context-free grammar.
www.info.ucl.ac.be /~pdupont/pdupont/bib/scfg.html   (211 words)

  
 Title page for ETD etd-05312001-133942
The objective of this research was to extract simple noun phrases from natural language texts using two different grammars: stochastic context-free grammar (SCFG) and non-statistical context free grammar (CFG).
Extraction of simple noun-phrases with the SCFG was accomplished using this probabilistic chart parser, a dictionary containing word probabilities along with the meaning, context-free grammar rules associated with rule probabilities and finally an algorithm to extract most likely parses of a sentence.
Extraction of Basic Noun Phrases from Natural Language Using Statistical Context-Free Grammar
scholar.lib.vt.edu /theses/available/etd-05312001-133942   (201 words)

  
 Corpora Jan 2003 to Mar 2003: [Corpora-List] Second Call for Pa
results over the issue of learning context-free grammars.
* Classes of context-free grammars for which positive learning
range of applications and are better described by context free
nora.hd.uib.no /corpora/2003-1/0485.html   (393 words)

  
 Plebius Press - Context free grammars
There is currently no entry for Context free grammars.
Talk about Context free grammars in our forums!
Differentiating parent practices related to adolescent behavior in the free time context.
psychology.plebius.org /encyclopedia.php?term=Context+free+grammars   (393 words)

  
 Probabilistic Context Free Grammars
Probabilistic context free grammars are implemented by the
It generates the same set of parses for a text that the corresponding context free grammar does, and assigns a probability to each parse.
) is a context free grammar that associates a probability with each of its productions.
nltk.sourceforge.net /tutorial/pcfg/section-pcfg.html   (393 words)

  
 BioMed Central Full text Evaluation of several lightweight stochastic context-free grammars for RNA secondary structure prediction
That is, instead of scoring a G-C pair stacked on a C-G base pair by adding a term for the free energy contribution of the GC/CG stack, an SCFG would add a log probability that GC/CG stacks are observed in known RNA structures.
Because some of the sources of his structure data were privileged, Mathews could not grant us permission to freely distribute this benchmark set (which is why we report performance results on a new benchmark set we are comfortable distributing).
The ANSI C source code for these implementations is freely available under the GNU General Public License (GPL) from http://www.genetics.wustl.edu/eddy/publications/#DowellEddy04.
www.biomedcentral.com /1471-2105/5/71   (393 words)

  
 Context free schemas for data-XML
refers to context free grammars, on which this proposal is based.
A context free grammar (CFG) is often the most compact and easiest way to describe some structure.
Not all languages (or structures) are context free, but it is usually worth the trouble making them so (or nearly).
www.w3.org /People/Bos/Schema/schemas   (393 words)

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