John C. Hogge
Research in domain independent planning has concentrated on making desired facts (goals) become true, with less attention on preventing undesired facts (negative goals) from becoming true. This document presents preliminary work towards a temporal-based model of prevention, based on Allen and Koomen’s temporal planner. The temporal model permits more expressive prevention problems and a more powerful prevention-oriented planner. Negative goals are temporally constrained-for instance, we can direct the planner to prevent a fact F from occurring before, after, or during a specific goal, between two temporally separated goals, etc. The planner can find solutions which allow F to become true at any time outside of the specified interval or which never allow F to become true. The temporal model permits the idea of delaying F after the interval, as well as terminating it before the interval. This paper describes a set of prevention techniques which have been implemented in a temporal planner and discusses necessary requirements for a more complete preventive planner.