Extending Unification Formalisms

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 solvers with the ProFIT typed feature system and these have been partially integrated into ALEP.