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.

Surface realisation: ambiguity and determinism

Abstract: Surface realisation is a subtask of natural language generation. It may be viewed as the inverse of parsing, that is, given a grammar and a representation of meaning, the surface realiser produces a natural language string that is associated by the grammar to the input meaning. Here, we present GenI, a surface realiser for Feature-Based Lexicalised Tree Adjoining Grammar (FB-LTAG) and three major extensions. The first extension improves the efficiency of the realiser with respect to lexical ambiguity. It is an adaptation from parsing of the "electrostatic tagging" optimisation, in which lexical items are associated with a set of polarities, and combinations of those items with non-neutral polarities are filtered out. The second extension deals with the number of outputs returned by the realiser. Normally, the GenI algorithm returns all of the sentences associated with the input logical form. Whilst these inputs can be seen as having the same core meaning, they often convey subtle distinctions in emphasis or style. It is important for generation systems to be able to control these extra factors. Here, we show how the input specification can be augmented with annotations that provide for the fine-grained control that is required. The extension builds off the fact that the FB-LTAG grammar used by the generator was constructed from a "metagrammar", explicitly putting to use the linguistic generalisations that are encoded within. The final extension provides a means for the realiser to act as a metagrammar-debugging environment. Mistakes in the metagrammar can have widespread consequences for the grammar. Since the realiser can output all strings associated with a semantic input, it can be used to find out what these mistakes are, and crucially, their precise location in the metagrammar.

Random Context Picture Grammars: The State of the Art

Abstract: We present a summary of results on random context picture grammars (rcpgs), which are a method of syntactic picture generation. The productions of such a grammar are context-free, but their appli- cation is regulated|permitted or forbidden|by context randomly dis- tributed in the developing picture. Thus far we have investigated three important subclasses of rcpgs, namely random permitting context pic- ture grammars, random forbidding context picture grammars and table- driven context-free picture grammars. For each subclass we have proven characterization theorems and shown that it is properly contained in the class of rcpgs. We have also developed a characterization theorem for all picture sets generated by rcpgs, and used it to nd a set that cannot be generated by any rcpg.

Methods for obtaining corresponding phrase structure and dependency grammars

Abstract: Two methods are given for converting grammars belonging to different systems. One converts a simple (context-free) phrase structure grammar (SPG) into a corresponding dependency grammar (DG); the other converts a DG into a corresponding SPG. The structures assigned to a string by a source grammar will correspond systematically, though a symmetrically, to those assigned by the target grammar resulting from its conversion. Since both systems are weakly equivalent, generating exactly the CF languages, the methods facilitate experimentation with either notation in devising rules for any CF language or any CF set of strings designed to undergo subsequent transformation.

Extended cross-serial dependencies in Tree Adjoining Grammars

Abstract: The ability to represent cross-serial dependencies is one of the central features of Tree Adjoining Grammar (TAG). The class of dependency structures representable by lexicalized TAG derivations can be captured by two graph-theoretic properties: a bound on the gap degree of the structures, and a constraint called well-nestedness. In this paper, we compare formalisms from two strands of extensions to TAG in the context of the question, how they behave with respect to these constraints. In particular, we show that multi-component TAG does not necessarily retain the well-nestedness constraint, while this constraint is inherent to Coupled Context-Free Grammar (Hotz and Pitsch, 1996).