Compacting the Penn Treebank Grammar

Treebanks, such as the Penn Treebank (PTB), offer a simple approach to obtaining a broad coverage grammar: one can simply read the grammar off the parse trees in the treebank. While such a grammar is easy to obtain, a square-root rate of growth of the rule set with corpus size suggests that the derived grammar is far from complete and that much more treebanked text would be required to obtain a complete grammar, if one exists at some limit. However, we offer an alternative explanation in terms of the underspecification of structures within the treebank. This hypothesis is explored by applying an algorithm to compact the derived grammar by eliminating redundant rules - rules whose right hand sides can be parsed by other rules. The size of the resulting compacted grammar, which is significantly less than that of the full treebank grammar, is shown to approach a limit. However, such a compacted grammar does not yield very good performance figures. A version of the compaction algorithm ta...

• Type: Conference
• Year: 1998
• Where: ACL
• Authors: Alexander Krotov, Mark Hepple, Robert J. Gaizauskas, Yorick Wilks
• Keywords: ACL 1998, ACL 2007, Broad Coverage Grammar, Compacted Grammar, Grammar