Showing papers on "Tree-adjoining grammar published in 1996"

Tree-bank Grammars

Abstract: By a "tree-bank grammar" we mean a context-free grammar created by reading the production rules directly from hand-parsed sentences in a tree bank. Common wisdom has it that such grammars do not perform we & though we know of no published data on the issue. The primary purpose of this paper is to show that the common wisdom is wrong. In particular, we present results on a tree-bank grammar based on the Penn WaII Street Journal tree bank. To the best of our knowledge, this grammar outperforms ah other non-word-based statistical parsers/grammars on this corpus. That is, it outperforms parsers that consider the input as a string of tags and ignore the actual words of the corpus.

Emergence of net-grammar in communicating agents

Abstract: Evolution of symbolic language and grammar is studied in a network model. Language is expressed by words, i.e. strings of symbols, which are generated by agents with their own symbolic grammar system. Agents communicate with each other by deriving and accepting words via rewriting rule set. They are ranked according to their communicative effectiveness: an agent which can derive less frequent and less acceptable words and accept words in less computational time will have higher scores. They can evolve by mutational processes, which change rewriting rules in their symbolic grammars. Complexity and diversity of words increase in the course of time. The emergence of modules and loop structure enhances the evolution. On the other hand, ensemble structure lead to a net-grammar, restricting individual grammars and their evolution.

Coordination in Tree Adjoining Grammars: Formalization and Implementation

Abstract: In this paper we show that an account for coordination can be constructed using the derivation structures in a lexicalized Tree Adjoining Grammar (LTAG). We present a notion of derivation in LTAGs that preserves the notion of fixed constituency in the LTAG lexicon while providing the flexibility needed for coordination phenomena. We also discuss the construction of a practical parser for LTAGs that can handle coordination including cases of non-constituent coordination.

Coordination in Tree Adjoining Grammars: formalization and implementation

Abstract: In this paper we show that an account for coordination can be constructed using the derivation structures in a lexicalized Tree Adjoining Grammar (LTAG). We present a notion of derivation in LTAGs that preserves the notion of fixed constituency in the LTAG lexicon while providing the flexibility needed for coordination phenomena. We also discuss the construction of a practical parser for LTAGs that can handle coordination including cases of non-constituent coordination.

Symbol-Relation Grammars

Abstract: A common approach to the formal description of pictorial and visual languages makes use of formal grammars and rewriting mechanisms. The present paper is concerned with the formalism of Symbol?Relation Grammars (SR grammars, for short). Each sentence in an SR language is composed of a set of symbol occurrences representing visual elementary objects, which are related through a set of binary relational items. The main feature of SR grammars is the uniform way they use context-free productions to rewrite symbol occurrences as well as relation items. The clearness and uniformity of the derivation process for SR grammars allow the extension of well-established techniques of syntactic and semantic analysis to the case of SR grammars. The paper provides an accurate analysis of the derivation mechanism and the expressive power of the SR formalism. This is necessary to fully exploit the capabilities of the model. The most meaningful features of SR grammars as well as their generative power are compared with those of well-known graph grammar families. In spite of their structural simplicity, variations of SR grammars have a generative power comparable with that of expressive classes of graph grammars, such as the edNCE and the N-edNCE classes.

Conditional attribute grammars

Abstract: Attribute grammars are a useful formalism for the specification of computations on structured terms. The classical definition of attribute grammars, however, has no way of treating conditionals nonstrictly. Consequently, the natural way of expressing many otherwise well-behaved computations involves a circularity. This article presents conditional attribute grammars, and extension of attribute grammars that enables more precise analysis of conditionals. In conditional attribute grammars, attribute equations may have guards. Equations are active only when their guards are satisfied. The standard attribute grammar evaluation classes are definable for conditional attribute grammars, and the corresponding evaluation techniques can be easily adapted. However, determining membership in standard evaluation classes such as 1-SWEEP, OAG, and SNC is NP-hard.

Growth transformations for probabilistic functions of stochastic grammars

Abstract: Stochastic Grammars are the most usual models in Syntactic Pattern Recognition. Both components of a Stochastic Grammar, the characteristic grammar and the probabilities attached to the rules, can be learnt automatically from training samples. In this paper, first a review of some algorithms are presented to infer the probabilistic component of Stochastic Regular and Context-Free Grammars under the framework of the Growth Transformations. On the other hand, with Stochastic Grammars, the patterns must be represented as strings over a finite set of symbols. However, the most natural representation in many Syntactic Pattern Recognition applications (i.e. speech) is as sequences of vectors from a feature vector space, that is, a continuous representation. Therefore, to obtain a discrete representation of the patterns, some quantization errors are introduced in the representation process. To avoid this drawback, a formal presentation of a semi-continuous extension of the Stochastic Regular and Context-Free Grammars is studied and probabilistic estimation algorithms are developed in this paper. In this extension, sequences of vectors, instead of strings of symbols, can be processed with Stochastic Grammars.

Paying Heed to Collocations

Abstract: : In this paper, we introduce a system, Sentence Planning Using Description, which generates collocations within the paradigm of sentence planning SPUD simultaneously constructs the semantics and syntax of a sentence using a Lexicalized Tree Adjoining Grammar (LTAG). This approach captures naturally and elegantly the interaction between pragmatic and syntactic constraints on descriptions in a sentence, and the inferential and lexical interactions between multiple descriptions in a sentence. At the same time, it exploits linguistically motivated, declarative specifications of the discourse functions of syntactic constructions to make contextually appropriate syntactic choices.

Dynamic Attribute Grammars

Abstract: Although Attribute Grammars were introduced long ago, their lack of expressiveness has resulted in limited use outside the domain of static language processing With the new notion of Dynamic Attribute Grammars defined on top of Grammar Couples, we show that it is possible to extend this expressiveness and to describe computations on structures that are not just trees, but also on abstractions allowing for infinite structures The result is a language that is comparable in power to most first-order functional languages, with a distinctive declarative character

Disambiguating grammars by exclusion of sub-parse trees

Abstract: A method is presented for disambiguation of grammars, based on the idea of excluding certain forbidden sub-parse trees. Combined with recent developments in the theory of parser generation for ambiguous grammars, the method disambiguates large classes of grammars guaranteeing that the generated language is unchanged.

Quantitative Constraint Logic Programming for Weighted Grammar Applications

Abstract: Constraint logic grammars provide a powerful formalism for expressing complex logical descriptions of natural language phenomena in exact terms. Describing some of these phenomena may, however, require some form of graded distinctions which are not provided by such grammars. Recent approaches to weighted constraint logic grammars attempt to address this issue by adding numerical calculation schemata to the deduction scheme of the underlying CLP framework.

Mild context-sensitivity and tuple-based generalizations of context-free grammar

Abstract: This paper classifies a family of grammar formalisms that extend context-free grammar by talking about tuples of terminal strings, rather than independently combining single terminal words into larger single phrases. These include a number of well-known formalisms, such as head grammar and linear context-free rewriting systems, but also a new formalism, (simple) literal movement grammar, which strictly extends the previously known formalisms, while preserving polynomial time recognizability. The descriptive capacity of simple literal movement grammars is illustrated both formally through a weak generative capacity argument and in a more practical sense by the description of conjunctive cross-serial relative clauses in Dutch. After sketching a complexity result and drawing a number of conclusions from the illustrations, it is then suggested that the notion of mild context-sensitivity currently in use, that depends on the rather loosely defined concept of constant growth, needs a modification to apply sensibly to the illustrated facts; an attempt at such a revision is proposed.

Grammars for Machine Design

Abstract: The use of grammars in mechanical design research is growing in popularity, largely due to the ability of a grammar to concisely express a language of designs. It is natural to attempt to achieve the level of success at writing descriptive languages for mechanical devices as is seen with spatial grammars in describing architectural styles. However, the differences in representing form and function between the fields and the mechanical designer’s focus on function must impact the type of grammars that can be used in describing mechanical designs. Two grammars for mechanical configuration design are briefly described: a string grammar for the design of cordless power drills and a graph grammar for the design of rolling carts. The ability of the grammars to generate a space of machine designs is discussed. How a mechanical design grammar can provide a platform for a designer assistance tool and the strengths and weaknesses of such a tool are presented.

(Un-)decidability of geometric properties of pictures generated by collage grammars

Abstract: Collage grammars are based on hyperedge replacement in a geometric environment and provide context-free syntactic devices for the generation of picture languages. An intriguing question is which geometric properties of the generated pictures can be decided by inspecting the generating collage grammars. The results presented in this paper address the question in two respects. (1) The decidability results known for hyperedge replacement grammars generating graph languages, based on the notion of compatibility, can be carried over to collage grammars. Unfortunately, compatible properties seem rare in the geometric setting. In this paper three concrete ones are presented. (2) In some other cases being only a minor extensions of situations for which compatibility is obtained, we can prove undecidability results.

Learning restricted probabilistic link grammars

Abstract: We describe a language model employing a new headed-disjuncts formulation of Lafferty et al.'s (1992) probabilistic link grammar, together with (1) an EM training method for estimating the probabilities, and (2) a procedure for learning some simple lexicalized grammar structures. The model in its simplest form is a generalization of n-gram models, but in its general form possesses context-free expressiveness. Unlike the original experiments on probabilistic link grammars, we assume that no hand-coded grammar is initially available (as with n-gram models). We employ untyped links to concentrate the learning on lexical dependencies, and our formulation uses the lexical identities of heads to influence the structure of the parse graph. After learning, the language model consists of grammatical rules in the form of a set of simple disjuncts for each word, plus several sets of probability parameters. The formulation extends cleanly toward learning more powerful context-free grammars. Several issues relating to generalization bias, linguistic constraints, and parameter smoothing are considered. Preliminary experimental results on small artificial corpora are supportive of our approach.

Visual conditional attributed rewriting systems in visual language specification

Abstract: In order to manage visual interaction problems, we deepen a formalisation of visual languages, based on the notion of visual sentence, introduced in a previous paper (Bottoni et al., 1995). Visual conditional attributed rewriting systems (vCARWs) are proposed for the specification of visual languages. We argue that vCARWs can be viewed as a generalisation of conditional set rewrite systems, which in turn were shown to be as expressive as textual context-free grammars, picture layout grammars, and constraint multiset grammars. Last, we outline a procedure to translate visual gestures into visual sentences according to vCARW rules.

Mild context-sensitivity and tuple-based generalizations of context-free grammar

Abstract: This paper classifies a family of grammar formalisms that extend context-free grammar by talking about tuples of terminal strings, rather than independently combining single terminal words into larger single phrases. These include a number of well-known formalisms, such as head grammar and linear context-free rewriting systems, but also a new formalism, (simple) literal movement grammar, which strictly extends the previously known formalisms, while preserving polynomial time recognizability. The descriptive capacity of simple literal movement grammars is illustrated both formally through a weak generative capacity argument and in a more practical sense by the description of conjunctive cross-serial relative clauses in Dutch. After sketching a complexity result and drawing a number of conclusions from the illustrations, it is then suggested that the notion of mild context-sensitivity currently in use, that depends on the rather loosely defined concept of constant growth, needs a modification to apply sensibly to the illustrated facts; an attempt at such a revision is proposed.

Viability of a Parsing Algorithm for Context-Sensitive Graph Grammars

Abstract: Graph Grammars describe formal languages similar to the textual ones commonly used to define computer languages, but their productions operate on graphs instead of on text. They are contextsensitive when productions rewrite patterns of symbols rather than single symbols. Parsing such grammars is inherently very hard because among other reasons, the input is not sequential in nature. An algorithm for parsing a large class of context-sensitive graph grammars has been developed by Jan Rekers and Andy Schurr. This thesis describes a first implementation of this algorithm as well as several improvements, additional work, examples, theory of operation and performance characteristics. Future and existing optimizations are discussed.

Direct automated inversion of logic grammars

Abstract: Reversibility of logic grammars in natural language processing is desirable for both theoretical and practical reasons. This paper addresses this topic in describing a new approach to automated inversion of logic grammars: the Direct Inversion Approach (dia). A logic grammar is inverted by automatically altering the order of literals in the grammar and reformulating certain recursive procedures at compile time. The inversion process results in a new executable grammar, which is evaluated top-down and left-to-right (using a standard Prolog interpreter), but not left-to-right with respect to the original grammar. Thedia improves upon related approaches not only in being fully automated and computationally tractable, but also with respect to the class of grammars it is able to invert and the performance of the new executable grammar produced.

Training stochastic grammars on semantical categories

Abstract: The evaluation of systems that parse natural language, on the basis of a score like bracketing accuracy or sentence accuracy, on an unseen text is becoming an important issue in grammar building and parsing. The statistical induction of grammars and the statistical training of (hand written) grammars are ways to attain or improve a score, but a stochastic grammar does not reflect the often stereotypical use of words depending on their semantical categories, often referred to as selectional restrictions or semantical patterns.

Attribute Grammars and Folds : Generic Control Operators

Abstract: Generic control operators, such as \emph{fold}, have been introduced in functional programming to increase the power and applicability of data-structure-based transformations This is achieved by making the structure of the data more explicit in program specifications We argue that this very important property is one of the original concepts of attribute grammars In this paper, we informally show the similarities between the fold formalism and attribute grammar specifications We also compare their respective method to eliminate the intermediate data structures introduced by function composition (notion of deforestation or fusion): the normalization algorithm for programs expressed with folds and the descriptional composition of attribute grammars Rather than identify the best way to achieve deforestation, the main goal of this paper is merely to intuitively present two programming paradigms to each other's supporting community and provide an unbiased account of their similarities and differences, in the hope that this leads to fruitful cross-fertilization