5,024 research outputs found
Principles and Implementation of Deductive Parsing
We present a system for generating parsers based directly on the metaphor of
parsing as deduction. Parsing algorithms can be represented directly as
deduction systems, and a single deduction engine can interpret such deduction
systems so as to implement the corresponding parser. The method generalizes
easily to parsers for augmented phrase structure formalisms, such as
definite-clause grammars and other logic grammar formalisms, and has been used
for rapid prototyping of parsing algorithms for a variety of formalisms
including variants of tree-adjoining grammars, categorial grammars, and
lexicalized context-free grammars.Comment: 69 pages, includes full Prolog cod
Evaluation of Computational Grammar Formalisms for Indian Languages
Natural Language Parsing has been the most prominent research area since the genesis of Natural Language Processing. Probabilistic Parsers are being developed to make the process of parser development much easier, accurate and fast. In Indian context, identification of which Computational Grammar Formalism is to be used is still a question which needs to be answered. In this paper we focus on this problem and try to analyze different formalisms for Indian languages
Left Recursion in Parsing Expression Grammars
Parsing Expression Grammars (PEGs) are a formalism that can describe all
deterministic context-free languages through a set of rules that specify a
top-down parser for some language. PEGs are easy to use, and there are
efficient implementations of PEG libraries in several programming languages.
A frequently missed feature of PEGs is left recursion, which is commonly used
in Context-Free Grammars (CFGs) to encode left-associative operations. We
present a simple conservative extension to the semantics of PEGs that gives
useful meaning to direct and indirect left-recursive rules, and show that our
extensions make it easy to express left-recursive idioms from CFGs in PEGs,
with similar results. We prove the conservativeness of these extensions, and
also prove that they work with any left-recursive PEG.
PEGs can also be compiled to programs in a low-level parsing machine. We
present an extension to the semantics of the operations of this parsing machine
that let it interpret left-recursive PEGs, and prove that this extension is
correct with regards to our semantics for left-recursive PEGs.Comment: Extended version of the paper "Left Recursion in Parsing Expression
Grammars", that was published on 2012 Brazilian Symposium on Programming
Language
An Abstract Machine for Unification Grammars
This work describes the design and implementation of an abstract machine,
Amalia, for the linguistic formalism ALE, which is based on typed feature
structures. This formalism is one of the most widely accepted in computational
linguistics and has been used for designing grammars in various linguistic
theories, most notably HPSG. Amalia is composed of data structures and a set of
instructions, augmented by a compiler from the grammatical formalism to the
abstract instructions, and a (portable) interpreter of the abstract
instructions. The effect of each instruction is defined using a low-level
language that can be executed on ordinary hardware.
The advantages of the abstract machine approach are twofold. From a
theoretical point of view, the abstract machine gives a well-defined
operational semantics to the grammatical formalism. This ensures that grammars
specified using our system are endowed with well defined meaning. It enables,
for example, to formally verify the correctness of a compiler for HPSG, given
an independent definition. From a practical point of view, Amalia is the first
system that employs a direct compilation scheme for unification grammars that
are based on typed feature structures. The use of amalia results in a much
improved performance over existing systems.
In order to test the machine on a realistic application, we have developed a
small-scale, HPSG-based grammar for a fragment of the Hebrew language, using
Amalia as the development platform. This is the first application of HPSG to a
Semitic language.Comment: Doctoral Thesis, 96 pages, many postscript figures, uses pstricks,
pst-node, psfig, fullname and a macros fil
Geometric representations for minimalist grammars
We reformulate minimalist grammars as partial functions on term algebras for
strings and trees. Using filler/role bindings and tensor product
representations, we construct homomorphisms for these data structures into
geometric vector spaces. We prove that the structure-building functions as well
as simple processors for minimalist languages can be realized by piecewise
linear operators in representation space. We also propose harmony, i.e. the
distance of an intermediate processing step from the final well-formed state in
representation space, as a measure of processing complexity. Finally, we
illustrate our findings by means of two particular arithmetic and fractal
representations.Comment: 43 pages, 4 figure
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Automatic Semantic Annotation of Music with Harmonic Structure
This paper presents an annotation model for harmonic structure of a piece of music, and a rule system that supports the automatic generation of harmonic annotations. Musical structure has so far received relatively little attention in the context of musical metadata and annotation, although it is highly relevant for musicians, musicologists and indirectly for music listeners. Activities in semantic annotation of music have so far mostly concentrated on features derived from audio data and file-level metadata. We have implemented a model and rule system for harmonic annotation as a starting point for semantic annotation of musical structure. Our model is for the musical style of Jazz, but the approach is not restricted to this style. The rule system describes a grammar that allows the fully automatic creation of an harmonic analysis as tree-structured annotations. We present a prototype ontology that defines the layers of harmonic analysis from chords symbols to the level of a complete piece. The annotation can be made on music in various formats, provided there is a way of addressing either chords or time points within the music. We argue that this approach, in connection with manual annotation, can support a number of application scenarios in music production, education, and retrieval and in musicology
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