This paper describes a structure-sharing method for the representation of complex phrase types in a parser for PATR-[I, a unification-based g r a m m a r formalism. In parsers for unification-based grammar formalisms, complex phrase types are derived by incremental refinement of rite phrase types defined in grammar rules and lexical entries. In a naive implementation, a new phrase type is built by copying older ones and then combining the copies according to the constraints stated in a grammar rule. .
