Are Very Large Context-Free Grammars Tractable?

In this paper, we present a method which, in practice, allows to use parsers for languages defined by very large context-free grammars (over a million symbol occurrences). The idea is to split the parsing process in two passes. A first pass computes a sub-grammar which is a specialized part of the large grammar selected by the input text and various filtering strategies. The second pass is a traditional parser which works with the sub-grammar and the input text. This approach is validated by practical experiments performed on a Earley-like parser running on a test set with two large context-free grammars.