Early Warnings of Plan Failure, Falso Positives and Envelopes: Experiments and a Model

We analyze a tradeoff between early warnings of plan failures and false positives. In general, a decision rule that provides earlier warnings will also produce more false positives. Slack time envelopes are decision rules that warn of plan failures in our Phoenix system. Until now, they have been constructed according to ad hoc criteria. In this paper we show that good performance under different criteria can be achieved by slack time envelopes throughout the course of a plan, even though envelopes are very simple decision rules. We also develop a probabilistic model of plan progress, from which we derive an algorithm for constructing slack time envelopes that achieve desired tradeoffs between early warnings and falso positives. * This research was supported by DARPA contract F49620-89-C-00113, by AFOSR under an Intelligent Real-time Problem Solving Initiative, AFOSR-91-0067, by ONR under a University Research Initiative grant, ONR N00014-86-K-0764, and by Texas Instruments Corporation. Early Warnings of Plan Failures and False Positives Cohen, St. Amant and Hart Early Warnings of Plan Failure and False Positives Cohen, St. Amant and Hart