Generalizing Temporal Controllability

Michael D. Moffitt, Martha E. Pollack

In this paper, we focus on extending the expressive power of constraint-based temporal reasoning formalisms. We begin with the well-known Simple Temporal Problem with Uncertainty, and incorporate three extensions: prior observability, in which the values of uncontrollable events become known prior to their actual occurrence; partial shrinkage, in which an observation event triggers the reduction of a contingent temporal interval; and a generalization of partial shrinkage to requirement links, making it possible to express certain types of uncertainty that may arise even when the time points in a problem are themselves fully controllable. We describe levels of controllability in the resulting formalism, the Generalized STPU, and relate this formalism to related developments in disjunctive temporal reasoning. Throughout, we motivate our approach with simple, real-world examples that illustrate the limitations of existing formalisms and the flexibility of our proposed extensions.