Hear What I Mean [BBN, 1976]. Answers questions in the role of a travel agent, using a database of facts about trips and expenses.
This was the most demanding task of any of the ARPA SUR domains. All processing passed through the control strategy component which used knowledge sources as subroutines (in contrast to HEARSAY which has autonomous knowledge sources).
HWIM's organization permits more direct experimentation with control strategies -- manipulating, for example, how many word islands are generated, direction of expansion, and interaction of system components.