This report introduces an implemented scheme for generating target- language sentences using a compositional representation of meaning called lexical conceptual structure. Lexical conceptual structure facilitates two crucial operations associated with generation: lexical selection and syntactic realization. The compositional nature of the representation is particularly valuable for these two operations when semantically equivalent source-and-target-language words and phrases are structurally or thematically divergent. To determine the correct lexical items and syntactic realization associated with the surface form in such cases, the underlying lexical-semantic forms are systematically mapped to the target-language syntactic structures. The model described constitutes a lexical-semantic extension to UNITRAN.

This report describes the organization and content of lexical information required for the task of machine translation. In particular, the lexical-conceptual basis for UNITRAN, an implemented machine translation system, will be described. UNITRAN uses an underlying form called lexical conceptual structure to perform lexical selection and syntactic realization. Lexical word entries have two levels of description: the first is an underlying lexical-semantic representation that is derived from hierarchically organized primitives, and the second is a mapping from this representation to a corresponding syntactic structure. The interaction of these two levels will be discussed and the lexical selection and syntactic realization processes will be described.