a1 RUCL, University of Helsinki, Hallituskatu 11, SF-00100 Helsinki, Finland.
The present paper is an introduction to unification as a formalism for writing grammars for natural languages. The paper is structured as follows. Section 1 briefly describes the history and the current scene of unification based grammar formalisms. Sections 2–3 describe the basic design of current formalisms. Section 4 constitutes a tutorial introduction to a representative unification based grammar formalism, the D–PATR system of Karttunen (1986). Sections 5—6 consider extensions of the unification formalism and its limitations. Section 7 examines implementation questions and addresses the question of the computational complexity of unification. — Some notes on terminology.
* Sections 1-3 and 5-6 were written by Lauri Carlson and sections 4, 7, and 8 by Krister Linden.