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.

Non-context-free grammars generating context-free languages

Abstract: If G is a grammar such that in each non-context-free rule of G, the right side contains a string of terminals longer than any terminal string appearing between two nonterminals in the left side, then the language generated by G is context free. Six previous results follow as corollaries of this theorem.

Generalized lr parsing algorithm for boolean grammars

Abstract: The generalized LR parsing algorithm for context-free grammars is extended for the case of Boolean grammars, which are a generalization of the context-free grammars with logical connectives added to the formalism of rules. In addition to the standard LR operations, Shift and Reduce, the new algorithm uses a third operation called Invalidate, which reverses a previously made reduction. This operation makes the mathematical justification of the algorithm significantly different from its prototype. On the other hand, the changes in the implementation are not very substantial, and the algorithm still works in time O(n4).

Syntax and Semantics of It-Clefts: A Tree Adjoining Grammar Analysis

Abstract: In this paper, we examine two main approaches to the syntax and semantics of it-clefts as in 'It was Ohno who won': an expletive approach where the cleft pronoun is an expletive and the cleft clause bears a direct syntactic or semantic relation to the clefted constituent, and a discontinuous constituent approach where the cleft pronoun has a semantic content and the cleft clause bears a direct syntactic or semantic relation to the cleft pronoun. We argue for an analysis using Tree Adjoining Grammar (TAG) that captures the best of both approaches. We use Tree-Local Multi-Component Tree Adjoining Grammar to propose a syntax of it-clefts and Synchronous Tree Adjoining Grammar (STAG) to define a compositional semantics on the proposed syntax. It will be shown that the distinction TAG makes between the derivation tree and the derived tree, the extended domain of locality characterizing TAG and the direct syntax-semantics mapping characterizing STAG allow for a simple and straightforward account of the syntax and semantics of it-clefts, capturing the insights and arguments of both the expletive and the discontinuous constituent approaches. Our analysis reduces the syntax and semantics of it-clefts to copular sentences containing definite description subjects, such as 'The person that won is Ohno'. We show that this is a welcome result, as evidenced by the syntactic and semantic similarities between it-clefts and the corresponding copular sentences.

Efficient Parsing for Transducer Grammars

Abstract: The tree-transducer grammars that arise in current syntactic machine translation systems are large, flat, and highly lexicalized. We address the problem of parsing efficiently with such grammars in three ways. First, we present a pair of grammar transformations that admit an efficient cubic-time CKY-style parsing algorithm despite leaving most of the grammar in n-ary form. Second, we show how the number of intermediate symbols generated by this transformation can be substantially reduced through binarization choices. Finally, we describe a two-pass coarse-to-fine parsing approach that prunes the search space using predictions from a subset of the original grammar. In all, parsing time reduces by 81%. We also describe a coarse-to-fine pruning scheme for forest-based language model reranking that allows a 100-fold increase in beam size while reducing decoding time. The resulting translations improve by 1.3 BLEU.