Jack forgot his wallet. 2b Sam did too. How can we refer to such an object - in effect a constant whose identity is unknown to us. Generating Discourse Entities Discourse entities are generated for each noun phrase. The history list is a list of discourse entities generated by the preceding sentences, with the most recent listed first.
Some systems retain just the last two or three sentences, while some let the list grow indefinitely.
The DEs evoked by each sentence are referred to as a local context . Constraints include number, gender, and more complex grammatical phenomena such as the rules for the use of reflexive pronouns. Jack ate it. Definite Descriptions Similar techniques will often work with definite descriptions. The phrase the car behaves somewhat like an it with the constraint of being of type car .