Integration of two stochastic context-free grammars can be useful in two pass approaches used, for example, in speech recognition and understanding. Based on an algorithm proposed by [Nederhof and Satta, 2002] for the non-probabilistic case, left-to-right strategies for the search for the best solution based on CKY and Earley parsers are discussed. The restriction that one of the two grammars m...

This survey paper describes several extensions of context-free grammars as defined in the Chomsky hierarchy. These augmentations use a variety of different strategies to create grammars that generate all context-free and some context-sensitive languages. The basic concepts of each of these extensions will be examined, as well as whether the enhanced grammars inherited some of the desirable prop...

We show how to encode context-free string grammars, linear contextfree tree grammars, and linear context-free rewriting systems as Abstract Categorial Grammars. These three encodings share the same constructs, the only difference being the interpretation of the composition of the production rules. It is interpreted as a first-order operation in the case of context-free string grammars, as a sec...

In this paper, we propose a new framework for online handwritten mathematical expression recognition. In this approach, we consider handwritten mathematical expressions as the output of stroke generation processes based on a stochastic context-free grammar which generates handwritten expressions stochastically. We estimate the most likely expression candidate derived from the grammar, rather th...

We propose a class trigram language model in which each class is specified by a stochastic context-free grammar. We show how to estimate the parameters of the model, and how to smooth these estimates. We present experimental perplexity and speech recognition results.

The present paper introduces and discusses generalized scattered context grammars that are based upon sequences of productions whose left-hand sides are formed by nonterminal strings, not just single nonterminals. It places two restrictions on the derivations in these grammars. More specifically, let k be a positive integer. The first restriction requires that all rewritten symbols occur within...

We discuss some of the practical issues that arise from decoding with general synchronous context-free grammars. We examine problems caused by unary rules and we also examine how virtual nonterminals resulting from binarization can best be handled. We also investigate adding more flexibility to synchronous context-free grammars by adding glue rules and phrases.

Many context aware systems assume that the context information they use is highly accurate. In reality, however, perfect and reliable context information is hard if not impossible to obtain. Several researchers have therefore argued that proper feedback such as monitor and control mechanisms have to be employed in order to make context aware systems applicable and useable in scenarios of realis...

Probabilistic context-free grammars have the unusual property of not always defining tight distributions (i.e., the sum of the “probabilities” of the trees the grammar generates can be less than one). This paper reviews how this non-tightness can arise and discusses its impact on Bayesian estimation of PCFGs. We begin by presenting the notion of “almost everywhere tight grammars” and show that ...

Context awareness is a vital element in pervasive and ubiquitous systems. While most existing research has focused on designing context-aware systems to integrate into the environment, less attention has been placed on the interoperability among the entities comprising such systems. In this paper, we consider how the components of a context-aware system can collaborate to achieve a common goal....