This paper reviews discourse phenomena that occur frequently in dialogs, reporting on a~n empirical study that demonstrates the necessity of handling ellipsis, anaphora, extragrammaticality, inter-sentential metalanguage, and other abbreviatory devices in order to achieve convivial user interaction. Invariably, users prefer to generate terse or fragmentary utterances instead of longer, more complete "standalone" expressions, even when given clear instructions tO the contrary. The XCALIBUR exbert system interface is designed to meet these needs, including generalized ellipsis resolution by means of a rule-based caseframe method superior tO previous semantic grammar approaches. .
