Tree-adjoining grammar

About: Tree-adjoining grammar is a research topic. Over the lifetime, 2491 publications have been published within this topic receiving 57813 citations.

Unsupervised Methods for Head Assignments

Abstract: We present several algorithms for assigning heads in phrase structure trees, based on different linguistic intuitions on the role of heads in natural language syntax. Starting point of our approach is the observation that a head-annotated treebank defines a unique lexicalized tree substitution grammar. This allows us to go back and forth between the two representations, and define objective functions for the unsupervised learning of head assignments in terms of features of the implicit lexicalized tree grammars. We evaluate algorithms based on the match with gold standard head-annotations, and the comparative parsing accuracy of the lexicalized grammars they give rise to. On the first task, we approach the accuracy of hand-designed heuristics for English and inter-annotation-standard agreement for German. On the second task, the implied lexicalized grammars score 4% points higher on parsing accuracy than lexicalized grammars derived by commonly used heuristics.

Some problems of finite representability

Abstract: It has been pointed out that context-free grammars of a certain class have the property that a one-one mapping exists between the structural descriptions of its sentences and the sentences generated by a finite state grammar. Given a grammar, it is decidable whether it belongs to this specific class or not. The grammars of this class can be divided into a countable hierarchy of increasing complexity.

Bisimulation Equivalences for Graph Grammars

Abstract: Along the years the concurrent behaviour of graph grammars has been widely investigated, and, in particular, several classical approaches to the semantics of Petri nets have been extended to graph grammars. Most of the existing semantics for graph grammars provide a (possibly concurrent) operational model of computation, while little interest has been devoted to the definition of abstract observational semantics. The aim of this paper is to introduce and study a behavioural equivalence over graph grammars, inspired by the classical history preserving bisimulation. Several choices are conceivable according to the kind of concurrent observation one is interested in. We concentrate on the basic case where the concurrent nature of a graph grammar computation is described by means of a prime event structure. As it happens for Petri nets, history preserving bisimulation can be studied in the general framework of causal automata -- a variation of ordinary automata introduced to deal with history dependent formalisms. In particular, we prove that history preserving bisimulation is decidable for finite-state graph grammars, by showing how the problem can be reduced to deciding the equivalence of finite causal automata.

Affix Grammars for Programming Languages

Abstract: Affix Grammars are members of the family of Two-Level Grammars, along with W-grammars, Metamorphosis Grammars and Attribute Grammars. In this tutorial we shall be concerned with the nature and rationale of Affix Grammars and their application in describing programming languages. Some parsing and affix evaluation methods for deterministic and nondeterministic Affix Grammars are discussed. By means of an example, a comparison is made with W-grammars and Attribute Grammars.