3,181 research outputs found
On the structure of context-sensitive grammars
Context sensitive grammar and generation of noncontext free language
Probabilistic mathematical formula recognition using a 2D context-free graph grammar
We present a probabilistic framework for the mathematical expression recognition problem. The developed system is flexible in that its grammar can be extended easily thanks to its graph grammar which eliminates the need for specifying rule precedence. It is also optimal in the sense that all possible interpretations of the expressions are expanded without making early commitments or hard decisions. In this paper, we give an overview of the whole system and describe in detail the graph grammar and the parsing process used in the system, along with some preliminary results on character, structure and expression recognition performances
An Efficient Probabilistic Context-Free Parsing Algorithm that Computes Prefix Probabilities
We describe an extension of Earley's parser for stochastic context-free
grammars that computes the following quantities given a stochastic context-free
grammar and an input string: a) probabilities of successive prefixes being
generated by the grammar; b) probabilities of substrings being generated by the
nonterminals, including the entire string being generated by the grammar; c)
most likely (Viterbi) parse of the string; d) posterior expected number of
applications of each grammar production, as required for reestimating rule
probabilities. (a) and (b) are computed incrementally in a single left-to-right
pass over the input. Our algorithm compares favorably to standard bottom-up
parsing methods for SCFGs in that it works efficiently on sparse grammars by
making use of Earley's top-down control structure. It can process any
context-free rule format without conversion to some normal form, and combines
computations for (a) through (d) in a single algorithm. Finally, the algorithm
has simple extensions for processing partially bracketed inputs, and for
finding partial parses and their likelihoods on ungrammatical inputs.Comment: 45 pages. Slightly shortened version to appear in Computational
Linguistics 2
Tree transducers, L systems, and two-way machines
A relationship between parallel rewriting systems and two-way machines is investigated. Restrictions on the ācopying powerā of these devices endow them with rich structuring and give insight into the issues of determinism, parallelism, and copying. Among the parallel rewriting systems considered are the top-down tree transducer; the generalized syntax-directed translation scheme and the ETOL system, and among the two-way machines are the tree-walking automaton, the two-way finite-state transducer, and (generalizations of) the one-way checking stack automaton. The. relationship of these devices to macro grammars is also considered. An effort is made .to provide a systematic survey of a number of existing results
Towards Zero-Overhead Disambiguation of Deep Priority Conflicts
**Context** Context-free grammars are widely used for language prototyping
and implementation. They allow formalizing the syntax of domain-specific or
general-purpose programming languages concisely and declaratively. However, the
natural and concise way of writing a context-free grammar is often ambiguous.
Therefore, grammar formalisms support extensions in the form of *declarative
disambiguation rules* to specify operator precedence and associativity, solving
ambiguities that are caused by the subset of the grammar that corresponds to
expressions.
**Inquiry** Implementing support for declarative disambiguation within a
parser typically comes with one or more of the following limitations in
practice: a lack of parsing performance, or a lack of modularity (i.e.,
disallowing the composition of grammar fragments of potentially different
languages). The latter subject is generally addressed by scannerless
generalized parsers. We aim to equip scannerless generalized parsers with novel
disambiguation methods that are inherently performant, without compromising the
concerns of modularity and language composition.
**Approach** In this paper, we present a novel low-overhead implementation
technique for disambiguating deep associativity and priority conflicts in
scannerless generalized parsers with lightweight data-dependency.
**Knowledge** Ambiguities with respect to operator precedence and
associativity arise from combining the various operators of a language. While
*shallow conflicts* can be resolved efficiently by one-level tree patterns,
*deep conflicts* require more elaborate techniques, because they can occur
arbitrarily nested in a tree. Current state-of-the-art approaches to solving
deep priority conflicts come with a severe performance overhead.
**Grounding** We evaluated our new approach against state-of-the-art
declarative disambiguation mechanisms. By parsing a corpus of popular
open-source repositories written in Java and OCaml, we found that our approach
yields speedups of up to 1.73x over a grammar rewriting technique when parsing
programs with deep priority conflicts--with a modest overhead of 1-2 % when
parsing programs without deep conflicts.
**Importance** A recent empirical study shows that deep priority conflicts
are indeed wide-spread in real-world programs. The study shows that in a corpus
of popular OCaml projects on Github, up to 17 % of the source files contain
deep priority conflicts. However, there is no solution in the literature that
addresses efficient disambiguation of deep priority conflicts, with support for
modular and composable syntax definitions
12th International Workshop on Termination (WST 2012) : WST 2012, February 19ā23, 2012, Obergurgl, Austria / ed. by Georg Moser
This volume contains the proceedings of the 12th International Workshop on Termination (WST 2012), to be held February 19ā23, 2012 in Obergurgl, Austria. The goal of the Workshop on Termination is to be a venue for presentation and discussion of all topics in and around termination. In this way, the workshop tries to bridge the gaps between different communities interested and active in research in and around termination. The 12th International Workshop on Termination in Obergurgl continues the successful workshops held in St. Andrews (1993), La Bresse (1995), Ede (1997), Dagstuhl (1999), Utrecht (2001), Valencia (2003), Aachen (2004), Seattle (2006), Paris (2007), Leipzig (2009), and Edinburgh (2010). The 12th International Workshop on Termination did welcome contributions on all aspects of termination and complexity analysis. Contributions from the imperative, constraint, functional, and logic programming communities, and papers investigating applications of complexity or termination (for example in program transformation or theorem proving) were particularly welcome. We did receive 18 submissions which all were accepted. Each paper was assigned two reviewers. In addition to these 18 contributed talks, WST 2012, hosts three invited talks by Alexander Krauss, Martin Hofmann, and Fausto Spoto
COSMICAH 2005: workshop on verification of COncurrent Systems with dynaMIC Allocated Heaps (a Satellite event of ICALP 2005) - Informal Proceedings
Lisboa Portugal, 10 July 200
Two characterisation results of multiple context-free grammars and their application to parsing
In the first part of this thesis, a Chomsky-SchĆ¼tzenberger characterisation and an automaton characterisation of multiple context-free grammars are proved. Furthermore, a framework for approximation of automata with storage is described. The second part develops each of the three theoretical results into a parsing algorithm
On Language Processors and Software Maintenance
This work investigates declarative transformation tools in the context of software maintenance. Besides maintenance of the language specification, evolution of a software language
requires the adaptation of the software written in that language as well as the adaptation of the software that transforms software written in the evolving language. This co-evolution is studied to derive automatic adaptations of artefacts from adaptations of the language specification.
Furthermore, AOP for Prolog is introduced to improve maintainability of language specifications and derived tools.Die Arbeit unterstĆ¼tzt deklarative Transformationswerkzeuge
im Kontext der Softwarewartung. Neben der Wartung der
Sprachbeschreibung erfordert die Evolution einer Sprache
sowohl die Anpassung der Software, die in dieser Sprache geschrieben ist als auch die Anpassung der Software, die diese Software transformiert. Diese Koevolution wird untersucht, um automatische Anpassungen
von Artefakten von Anpassungen der Sprachbeschreibungen abzuleiten. Weiterhin wird AOP fĆ¼r Prolog eingefĆ¼hrt, um die Wartbarkeit von Sprachbeschreibungen und den daraus abgeleiteten Werkzeugen zu erhƶhen
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