TY - GEN
T1 - Highly constrained unification grammars
AU - Feinstein, Daniel
AU - Wintner, Shuly
PY - 2006
Y1 - 2006
N2 - 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. We then relax the constraint and show that one-reentrant unification grammars generate exactly the class of tree-adjoining languages. We thus relate the commonly used and linguistically motivated formalism of unification grammars to more restricted, computationally tractable classes of languages.
AB - 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. We then relax the constraint and show that one-reentrant unification grammars generate exactly the class of tree-adjoining languages. We thus relate the commonly used and linguistically motivated formalism of unification grammars to more restricted, computationally tractable classes of languages.
UR - http://www.scopus.com/inward/record.url?scp=84860501890&partnerID=8YFLogxK
U2 - 10.3115/1220175.1220312
DO - 10.3115/1220175.1220312
M3 - Conference contribution
AN - SCOPUS:84860501890
SN - 1932432655
SN - 9781932432657
T3 - COLING/ACL 2006 - 21st International Conference on Computational Linguistics and 44th Annual Meeting of the Association for Computational Linguistics, Proceedings of the Conference
SP - 1089
EP - 1096
BT - COLING/ACL 2006 - 21st International Conference on Computational Linguistics and 44th Annual Meeting of the Association for Computational Linguistics, Proceedings of the Conference
PB - Association for Computational Linguistics (ACL)
T2 - 21st International Conference on Computational Linguistics and 44th Annual Meeting of the Association for Computational Linguistics, COLING/ACL 2006
Y2 - 17 July 2006 through 21 July 2006
ER -