Structure Sharing and Parallelization in a GB Parser

By utilizing structure sharing among its parse trees, a GB parser can increase its efficiency dramatically. Using a GB parser which has as its phrase structure recovery component an implementation of Tomita's algorithm (as described in [Tom86]), we investigate how a GB parser can preserve the structure sharing output by Tomita's algorithm. In this report, we discuss the implications of using Tomita's algorithm in GB parsing, and we give some details of the structuresharing parser currently under construction. We also discuss a method of parallelizing a GB parser, and relate it to the existing literature on parallel GB parsing. Our approach to preserving sharing within a shared-packed forest is applicable not only to GB parsing, but anytime we want to preserve structure sharing in a parse forest in the presence of features.

A Minimal GB Parser

We describe a GB parser implemented along the lines of those written by Fong [4] and Dorr [2]. The phrase structure recovery component is an implementation of Tomita's generalized LR parsing algorithm (described in [10]), with recursive control flow (similar to Fong's implementation). The major principles implemented are government, binding, bounding, trace theory, case theory, θ-theory, and barriers. The particular version of GB theory we use is that described by Haegeman [5]. The parser is minimal in the sense that it implements the major principles needed in a GB parser, and has fairly good coverage of linguistically interesting portions of the English language.

A Hybrid GLR Algorithm for Parsing with Epsilon Grammars

We give a hybrid algorithm for parsing epsilon grammars based on Tomita's non-ϵ-grammar parsing algorithm ([Tom86]) and Nozohoor-Farshi's ϵ-grammar recognition algorithm ([NF91]). The hybrid parser handles the same set of grammars handled by Nozohoor-Farshi's recognizer. The algorithm's details and an example of its use are given. We also discuss the deployment of the hybrid algorithm within a GB parser, and the reason an ϵ grammar parser is needed in our GB parser.