In this paper, we present an alternative approach to multiple inheritance for typed feature structures. In our approach, a feature structure can be associated with several types coming from different hierarchies (dimensions). In case of multiple inheritance, a type has supertypes from different hierarchies. We contrast this approach with approaches based on a single type hierarchy where a feature structure has only one unique most general type, and multiple inheritance involves computation of greatest lower bounds in the hierarchy. The proposed approach supports current linguistic analyses in constraint-based formalisms like HPSG, inheritance in the lexicon, and knowledge representation for NLP systems. Finally, we show that multi-dimensional inheritance hierarchies can be compiled into a Prolog term representation, which allows to compute the conjunction of two types efficiently by Prolog term unification. 1

This paper describes some of the results of the project The Reusability of Grammatical Resources. The aim of the project is to extend current grammar formalisms with notational devices and constraint solvers in order to aid the development of reusable grammars. The project took the Advanced Linguistic Engineering Platform (ALEP) as its starting point. ALEP allows two levels of extension: additional syntactic expressions ("syntactic sugar") and specialised external constraint solvers. Our syntactic additions to ALEP comprise support for LFG coherence and completeness and an extended notation for phrase-structure rules. The project has developed solvers for set constraints, set operations, linear precedence constraints and guarded constraints. The extensions were formally specified and implemented as Prolog modules and hence have a wider applicability. These can be either used standalone or integrated within existing grammar formalisms. We have sucessfully integrated the all constraint s...