For any context-free grammar, we build a transition diagram, that is, a finite directed graph with labeled arcs, which describes the work of the grammar. This approach is new, and it is different from previously known graph models. We define the concept of proper walk in this transition diagram and we prove that a word belongs to a given context-free language if and only if this word can be obt...

We prove that the class of permutations generated by passing an ordered sequence 12 . . . n through a stack of depth 2 and an infinite stack in series is in bijection with an unambiguous context-free language, where a permutation of length n is encoded by a string of length 3n. It follows that the sequence counting the number of permutations of each length has an algebraic generating function. ...

Tree substitution grammars (TSGs) offer many advantages over context-free grammars (CFGs), but are hard to learn. Past approaches have resorted to heuristics. In this paper, we learn a TSG using Gibbs sampling with a nonparametric prior to control subtree size. The learned grammars perform significantly better than heuristically extracted ones on parsing accuracy.

A randomised polylog time algorithm is given for deciding whether or not the sets of words of a given length generated by two unam-biguous context-free grammars coincide. The algorithm is in randomised NC4 in terms of the product of the grammar size and the length.

This paper presents the pattern engine that is offered by the Ellogon language engineering platform. This pattern engine allows the application of context-free grammars over annotations, which are metadata generated during the processing of documents by natural language tools. In addition, grammar development is aided by a graphical grammar editor, giving grammar authors the capability to test

We present a phonological probabilistic contextfree grammar, which describes the word and syllable structure of German words. The grammar is trained on a large corpus by a simple supervised method, and evaluated on a syllabification task achieving 96.88% word accuracy on word tokens, and 90.33% on word types. We added rules for English phonemes to the grammar, and trained the enriched grammar o...

We survey work on the paradigm called “computing by observing.” Its central feature is that one considers the behavior of an evolving system as the result of a computation. To this end an observer records this behavior. It has turned out that the observed behavior of computationally simple systems can be very complex, when an appropriate observer is used. For example, a restricted version of co...

Ellul, Krawetz, Shallit and Wang prove an exponential lower bound on the size of any context-free grammar generating the language of all permutations over some alphabet. We generalize their method and obtain exponential lower bounds for many other languages, among them the set of all squares of given length, and the set of all words containing each symbol at most twice.

A machine translation system is said to be complete if all expressions that are correct according to the source-language grammar can be translated into the target language. This paper addresses the completeness issue for compositional machine translation in general, and for compositional machine translation of context-free grammars in particular. Conditions that guarantee translation completene...

In this paper we examine the problem of extracting schema-conforming metadata out from HTML sources. A technique founded on semistructured data analysis is explained. It is based on the combination of HTML styles, which abstract the visual characteristics of documents, and document-oriented context-free grammar, which provide structural information. This technique is flexible enough to be appli...