Thematic Roles

Elementary trees in TAGs capture several notions of locality, with the most primary of these being locality of -role assignment. Each elementary tree has associated with it the -roles assigned by the anchor of that elementary tree. In the current XTAG system, while the notion of locality of -role assignment within an elementary tree has been implicit, the -roles assigned by a head have not been explicitly represented in the elementary tree. Incorporating -role information will make the elementary trees more informative and will enable efficient pruning of spurious derivations when embedded into a specific context. In the case of a Synchronous TAG, -roles can also be used to automatically establish links between two elementary trees, one in the object language and one in the target language.