182 research outputs found
Structure preserving transformations on non-left-recursive grammars
We will be concerned with grammar covers, The first part of this paper presents a general framework for covers. The second part introduces a transformation from nonleft-recursive grammars to grammars in Greibach normal form. An investigation of the structure preserving properties of this transformation, which serves also as an illustration of our framework for covers, is presented
A survey of normal form covers for context-free grammars
An overview is given of cover results for normal forms of context-free grammars. The emphasis in this paper is on the possibility of constructing É›-free grammars, non-left-recursive grammars and grammars in Greibach normal form. Among others it is proved that any É›-free context-free grammar can be right covered with a context-free grammar in Greibach normal form. All the cover results concerning the É›-free grammars, the non-left-recursive grammars and the grammars in Greibach normal form are listed, with respect to several types of covers, in a cover-table
Context-Free Grammars: Covers, Normal Forms, and Parsing
This monograph develops a theory of grammatical covers, normal forms and parsing. Covers, formally defined in 1969, describe a relation between the sets of parses of two context-free grammars. If this relation exists then in a formal model of parsing it is possible to have, except for the output, for both grammars the same parser. Questions concerning the possibility to cover a certain grammar with grammars that conform to some requirements on the productions or the derivations will be raised and answered. Answers to these cover problems will be obtained by introducing algorithms that describe a transformation of an input grammar into an output grammar which satisfies the requirements. The main emphasis in this monograph is on transformations of context-free grammars to context-free grammars in some normal form. However, not only transformations of this kind will be discussed, but also transformations which yield grammars which have useful parsing properties
Inferring descriptive generalisations of formal languages
In the present paper, we introduce a variant of Gold-style learners that is not required to infer precise
descriptions of the languages in a class, but that must find descriptive patterns, i.e., optimal
generalisations within a class of pattern languages. Our first main result characterises those indexed
families of recursive languages that can be inferred by such learners, and we demonstrate that this
characterisation shows enlightening connections to Angluin’s corresponding result for exact inference.
Using a notion of descriptiveness that is restricted to the natural subclass of terminal-free
E-pattern languages, we introduce a generic inference strategy, and our second main result characterises
those classes of languages that can be generalised by this strategy. This characterisation
demonstrates that there are major classes of languages that can be generalised in our model, but not
be inferred by a normal Gold-style learner. Our corresponding technical considerations lead to deep
insights of intrinsic interest into combinatorial and algorithmic properties of pattern languages
Inferring descriptive generalisations of formal languages
In the present paper, we introduce a variant of Gold-style learners that is not
required to infer precise descriptions of the languages in a class, but that must
nd descriptive patterns, i. e., optimal generalisations within a class of pattern
languages. Our rst main result characterises those indexed families of recursive
languages that can be inferred by such learners, and we demonstrate that
this characterisation shows enlightening connections to Angluin's corresponding
result for exact inference. Furthermore, this result reveals that our model
can be interpreted as an instance of a natural extension of Gold's model of
language identi cation in the limit. Using a notion of descriptiveness that is
restricted to the natural subclass of terminal-free E-pattern languages, we introduce
a generic inference strategy, and our second main result characterises
those classes of languages that can be generalised by this strategy. This characterisation
demonstrates that there are major classes of languages that can be
generalised in our model, but not be inferred by a normal Gold-style learner.
Our corresponding technical considerations lead to insights of intrinsic interest
into combinatorial and algorithmic properties of pattern languages
Matrix Graph Grammars
This book objective is to develop an algebraization of graph grammars.
Equivalently, we study graph dynamics. From the point of view of a computer
scientist, graph grammars are a natural generalization of Chomsky grammars for
which a purely algebraic approach does not exist up to now. A Chomsky (or
string) grammar is, roughly speaking, a precise description of a formal
language (which in essence is a set of strings). On a more discrete
mathematical style, it can be said that graph grammars -- Matrix Graph Grammars
in particular -- study dynamics of graphs. Ideally, this algebraization would
enforce our understanding of grammars in general, providing new analysis
techniques and generalizations of concepts, problems and results known so far.Comment: 321 pages, 75 figures. This book has is publisehd by VDM verlag, ISBN
978-363921255
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