Spatial operators in natural language understanding: the prepositions

The paper describes the operation of a LISP program which accepts English sentences involving spatial prepositions and creates a three dimensional model of the objects described, with emphasis on the appropriate spatial relations between the objects. A sequence of such sentences can result in a fairly elaborate model. The program can then answer questions about the relationship of the objects, even though the relationship in question between two objects in the model may not have been explicit in the original description.