Daniel feinstein

Unification grammars are widely accepted as an expressive means for describing the structure of natural languages. In general, the recognition problem is undecidable for unification grammars. Even with restricted variants of the formalism, offline parsable grammars, the problem is computationally hard. We present two natural constraints on unification grammars which limit their expressivity. We first show that non-reentrant unification grammars generate exactly the class of contextfree languages.

8p hongvang_1 16-04-2013 40 1   Download