A proposal for modifications in the formalism of GPSG

Recent investigations how a remarkable conver-gence among contemporary unification-based formal-isms for syntactic description. This convergence is now itsel f becoming an object of study, and there is an increasing recognition of the need for explicit characterizations of the properties that relate and distinguish similar grammar formalisms. The paper proposes a series of changes in the for-malism of Generalized Phrase Structure Grammar that throw light on its relation to Functional Unifica-tion Grammar. The essential contribution is a generalization of cooccurrence restrictions, which become the principal and unifying device of GPSG. Introducing Category Cooccurrence Restrictions (CCRs) for lo-cal trees (in analogy to Feature Cooccurrence Re-strictions for categories) provides a genuine gain in expressiveness for the formalism. Other devices, such as Feature Instantiation Principles and Linear Precedence Statements can be regarded as special cases of CCRs. The proposals lead to a modified no-tion of unification i tsel f