Inference of regular grammars via skeletons

Radhakrishnan, V.; Nagaraja, G S

doi:10.1109/tsmc.1987.6499309

Cited by 32 publications

(9 citation statements)

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“…In actual fact, Radhakrishnan and Nagaraja [33,34] had already claimed a similar grammatical characterization for TDRL, but they gave no proof. Our grammatical definition of TDRL mainly adds point 3(a) to their definition, but this turns out to be an essential point in the equivalence proof.…”

Section: Terminal Distinguishable Right-linear Languagesmentioning

confidence: 99%

“…In a second part of the paper, we discuss questions concerning grammatical inference of these systems. More precisely, we show that PCGSTT whose component grammars are terminal distinguishable right-linear, a notion introduced by Radhakrishnan and Nagaraja in [33,34], are identifiable in the limit if certain data communication information is supplied in addition. …”

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confidence: 99%

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Parallel communicating grammar systems with terminal transmission

Fernau

2001

Acta Informatica

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We introduce a new variant of PC grammar systems, called PC grammar systems with terminal transmission, PCGSTT for short. We show that right-linear centralized PCGSTT have nice formal language theoretic properties: they are closed under gsm mappings (in particular, under intersection with regular sets and under homomorphisms) and union; a slight variant is, in addition, closed under concatenation and star; their power lies between that of n-parallel grammars introduced by Wood and that of matrix languages of index n, and their relation to equal matrix grammars of degree n is discussed. We show that membership for these language classes is complete for NL. In a second part of the paper, we discuss questions concerning grammatical inference of these systems. More precisely, we show that PCGSTT whose component grammars are terminal distinguishable right-linear, a notion introduced by Radhakrishnan and Nagaraja in [33,34], are identifiable in the limit if certain data communication information is supplied in addition.

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Section: Terminal Distinguishable Right-linear Languagesmentioning

confidence: 99%

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confidence: 99%

Parallel communicating grammar systems with terminal transmission

Fernau

2001

Acta Informatica

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“…As a consequence, the large body of research on inductive inference that originated from Gold's works has concentrated on the problem of finding restricted classes of regular grammars for which learning from positive data is possible. This research has led to the identification of several such classes [Angluin 1982;Radhakrishnan and Nagaraja 1987], which were proven to be identifiable in the limit, and for which unsupervised algorithms were developed and formally proven to be correct.…”

Section: Introductionmentioning

confidence: 99%

Automatic information extraction from large websites

Crescenzi

Mecca

2004

J. ACM

146

118

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Information extraction from websites is nowadays a relevant problem, usually performed by software modules called wrappers. A key requirement is that the wrapper generation process should be automated to the largest extent, in order to allow for large-scale extraction tasks even in presence of changes in the underlying sites. So far, however, only semi-automatic proposals have appeared in the literature.We present a novel approach to information extraction from websites, which reconciles recent proposals for supervised wrapper induction with the more traditional field of grammar inference. Grammar inference provides a promising theoretical framework for the study of unsupervised-that is, fully automatic-wrapper generation algorithms. However, due to some unrealistic assumptions on the input, these algorithms are not practically applicable to Web information extraction tasks.The main contributions of the article stand in the definition of a class of regular languages, called the prefix mark-up languages, that abstract the structures usually found in HTML pages, and in the definition of a polynomial-time unsupervised learning algorithm for this class. The article shows that, differently from other known classes, prefix mark-up languages and the associated algorithm can be practically used for information extraction purposes.A system based on the techniques described in the article has been implemented in a working prototype. We present some experimental results on known Websites, and discuss opportunities and limitations of the proposed approach.

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“…In this approach, tree-like descriptions of the words are given to the inference method. This description usually gives relevant information which is related to the training data, for instance, one of the possible ways the data can be generated [4]- [6]. These inference methods can be modified for inferring tree languages.…”

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confidence: 99%