User-Defined Nonmonotonicity in Unification-Based Formalisms

A common feature of recent unification-based grammar formalisms is that they give the user the ability to define his own structures. However, this possibility is mostly limited and does not include nonmonotonic operations. In this paper we show how nonmonotonic operations can also be user-defined by applying default logic (Reiter 1980) and generalizing previous results on nonmonotonic sorts (Young & Rounds 1993).