Default representation in constraint-based frameworks

Default unification has been used in several linguistic applications. Most of them have utilized defaults at a metalevel, as part of an extended description language. We propose that allowing default unification to be a fully integrated part of a typed feature structure system requires default unification to be a binary, order independent function, so that it acquires the perspicuity and declarativity familiar from normal unification-based frameworks. Furthermore, in order to respect the behaviour of defaults, default unification should allow default reentrancies and values on more general types to be overridden by conflicting default information on more specific types. We define what we believe is the first version of default unification to fully satisfy these criteria, and argue that it can improve the representation of a range of phenomena in syntax, semantics and the lexico-pragmatic interface.